Redirect to STDOUT Problem

[Jordan Glassman]

Trying to do something fairly routine... drop output into a file to
graph, but the following command at the bash command line:

ising output

produces a blinking cursor, an empty file named "output," and a
program that runs forever. With no redirect, the output is normal.
Below is the printf statement used to generate output.

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f \
Chi=%5.2f\n",beta,(energy/n2),(moment/n2), \
(summe2-summe*summe)/n2, \
(summm2-summm*summm)/n2);

I verified that things like 'ls output' work fine, and that I can
also redirect output from other c programs I've written. Something is
funny about this one.

Any thoughts?

[Ben Bacarisse]

Jordan Glassman <jo************@gmail.comwrites:

Trying to do something fairly routine... drop output into a file to
graph, but the following command at the bash command line:

ising output

On modern systems, . is often not in your path. Did you just forget
to type ./ising?

produces a blinking cursor, an empty file named "output," and a
program that runs forever. With no redirect, the output is normal.
Below is the printf statement used to generate output.

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f \
Chi=%5.2f\n",beta,(energy/n2),(moment/n2), \
(summe2-summe*summe)/n2, \
(summm2-summm*summm)/n2);

Nothing here can explain what is happening. The printf is correct.
Of course, if n2 == 0 you won't get any output but that will happen
with and without the redirect.

I verified that things like 'ls output' work fine, and that I can
also redirect output from other c programs I've written. Something is
funny about this one.

Any thoughts?

The problem is probably not in the C code. You need someone to watch
exactly what you are doing and they'll probably spot it in no time. I
think a group like comp.unix.programmer might be better.

--
Ben.

[Jordan Glassman]

Ben,

Thanks for the reply...

On modern systems, . is often not in your path. Did you just forget
to type ./ising?

No, that's not the problem.

Nothing here can explain what is happening. The printf is correct.
Of course, if n2 == 0 you won't get any output but that will happen
with and without the redirect.

The problem is probably not in the C code. You need someone to watch
exactly what you are doing and they'll probably spot it in no time. I
think a group like comp.unix.programmer might be better.

I tend to agree, but since *everything else* works except this
particular c program, which contains nothing more than a few
calculations inside loops and this one output statement, I decided to
post here first.

-j

[Peter Nilsson]

Jordan Glassman wrote:

...
I tend to agree, but since *everything else* works except this
particular c program, which contains nothing more than a few
calculations inside loops and this one output statement, I
decided to post here first.

Though for some reason you decided not to post the code.
Still, your loss...

--
Peter

[Jordan Glassman]

>

Though for some reason you decided not to post the code.
Still, your loss...

My loss? Here it is...

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <curses.h>

#include <unistd.h// ANSI C???

#define N 40
#define NITERS 5000000

void filllattice(int (*m)[N]);
void seed(void); /* bad bad bad */
void printlattice(int (*m)[N]);
void ising(int (*m)[N],double beta);

int main(){

int lattice[N][N];
double beta=0.0;

seed();

for(beta=0.5;beta<=1.2;beta+=0.01){

filllattice(lattice);

// clear();

// printlattice(lattice);

ising(lattice,beta);

}

return 0;

}

void filllattice(int (*m)[N]){

int i,j;

for(i=0;i<N;i++){
for(j=0;j<N;j++){
if((((float)rand()/(float)RAND_MAX)) 0.5) m[i][j]= 1;
else m[i][j] = -1;
}
}

}

void seed(void){

struct tm *mt;
int i;
time_t t;
char timestr[3];

t=time(NULL);
mt=localtime(&t);
strftime(timestr,3,"%S",mt);

srand(atoi(timestr));

}

void printlattice(int (*m)[N]){

int i,j;

/* system("clear"); */
move(0,0);

for(i=0;i<N;i++){
putchar('\n');
for(j=0;j<N;j++){
if(m[i][j]==1)printf(" 1");
else printf(" -1");
}
}

putchar('\n');
}

void ising(int (*m)[N],double beta){

int i,j,k;
double energy,moment;
double summe,summm,summe2,summm2;
int numsteps=0;
double sum_nn,sums;
double deltaH;
double sum_nnn;
int n2=N*N;
double half=NITERS/2;

k=0;

energy=moment=0.0;
summe=summm=summe2=summm2=0.0;

// pick a site randomly

for(i=0;i<N;i++){
for(j=0;j<N;j++){
moment += m[i][j];
energy -= 2*m[i][j]*(m[(i+1)%N][j]+m[i][(j+1)%N]+m[(i+1)%N][(j
+1)%N]/5);
}
}

for(k=0;k<NITERS;k++){

i=rand()%N;
j=rand()%N;

sum_nn=m[i][((j+1)%N)]+m[i][((j-1+N)%N)]+m[((i+1)%N)][j]+m[((i-1+N)
%N)][j];
sum_nnn=(m[((i+1)%N)][((j+1)%N)]+m[((i-1+N)%N)][((j-1+N)%N)]
+m[((i-1+N)%N)][((j+1)%N)]+m[((i+1)%N)][((j-1+N)%N)])/5;
sums=sum_nn+sum_nnn;
deltaH=m[i][j]*sums;
if((exp(-1.3*deltaH*beta))>((float)rand()/(float)RAND_MAX) ||
(deltaH < 0) ){
energy += 2*deltaH;
moment -= 2*m[i][j];
m[i][j] *= -1;
}

if(k>half){
summe+=energy;
summe2+=energy*energy;
summm+=moment;
summm2+=moment*moment;
}

/* if(k>10000){
k=0;
putchar('\n');
printf("E=%f m=%f",(energy/n2),(moment/n2));
printlattice(m);
sleep(1);
} */

}

summe /= half;
summe2 /= half;
summm /= half;
summm2 /= half;

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f Chi=%5.2f\n",beta,(energy/
n2),(moment/n2),(summe2-summe*summe)/n2,(summm2-summm*summm)/n2);

}

[Richard Heathfield]

Jordan Glassman said:

>>
Though for some reason you decided not to post the code.
[...]

[...] Here it is...

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <curses.h>

#include <unistd.h// ANSI C???

This // comment really screwed up my compiler. To answer your question
redoubled in spades, neither curses.h nor unistd.h are ANSI C. // comments
have become so officially (since 1999), but in practice almost nobody has
a compiler that conforms to C99 in *every* respect, so those of us who
prefer to use a conforming mode have no choice but to conform to an
earlier standard (C90 or C95), in which // is merely a syntax error. In
this case, my compiler saw // ANSI C??? as part of the filename to
include!

Anyway, that's easy enough to fix (I removed the comment!), but doing so
exposed a whole bunch of compilation issues with your code - dozens of
errors. Oddly, however, removing or replacing the remaining // comments
sorted most of these out. The remaining nits were:

int main(){

My compiler (rightly) prefers int main(void) rather than just int main(),
but really this is no big deal. You have the return type (int) exactly
right, and that's what matters here.

if((((float)rand()/(float)RAND_MAX)) 0.5)

The compiler says: "warning: cast does not match function type"

In almost all cases, a cast on a human being indicates a broken limb.
In almost all cases, a cast in a C program indicates a broken line.

In C, the normal way to do (pseudo) random numbers selected from N
possibilities (in the range 0 to N-1) is to get a value in the half-open
range [0, 1) like this:

rand() / (RAND_MAX + 1.0)

and then multiply by N to get a value in the half-open range [0, N).
It seems that you want a value in the half-open range [0, 1) so you can
omit the multiplication step:

if(rand() / (RAND_MAX + 1.0) 0.5)

(This happens in one other place in the code, too.)

Running this code gives me a bunch of results as follows:

B=0.50 E= -0.8500 m= -0.0325 Cv= 3.52 Chi= 9.21
B=0.51 E= -0.8225 m= 0.1338 Cv= 3.42 Chi=10.27
B=0.52 E= -0.8500 m= -0.1550 Cv= 3.65 Chi=13.73
B=0.53 E= -0.8100 m= 0.0325 Cv= 3.69 Chi=16.82
B=0.54 E= -0.8975 m= 0.0488 Cv= 3.72 Chi=13.67
B=0.55 E= -0.9200 m= -0.0088 Cv= 4.08 Chi=20.47
B=0.56 E= -0.9975 m= 0.0563 Cv= 4.18 Chi=19.43
B=0.57 E= -0.9525 m= 0.0125 Cv= 4.59 Chi=34.67
B=0.58 E= -1.1075 m= -0.1938 Cv= 4.12 Chi=22.44
B=0.59 E= -1.0425 m= 0.1288 Cv= 4.83 Chi=30.55
B=0.60 E= -1.0675 m= -0.1750 Cv= 5.23 Chi=38.14
B=0.61 E= -1.0475 m= -0.0775 Cv= 5.36 Chi=55.96
B=0.62 E= -1.1625 m= 0.2350 Cv= 4.85 Chi=87.07
B=0.63 E= -1.1850 m= -0.0050 Cv= 6.26 Chi=127.39

but it didn't appear to stop. I reduced NITERS from 5000000 to 5 and N from
40 to 4, and it worked just fine, producing 70 lines of output.
Redirection of stdout to a file named 'output' worked just fine with no
weirdities going on. Looks fine to me.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Ben Bacarisse]

Jordan Glassman <jo************@gmail.comwrites:

>Though for some reason you decided not to post the code.
Still, your loss...

My loss? Here it is...

Yes. I can now tell you how to get it to work (but
comp.unix.programmer is still the better place).

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <curses.h>

curses programs can't usually have their put redirected (ask in
c.u.p for when and why).

#include <unistd.h// ANSI C???

No, not ANSI C.

<snip>

void seed(void){

struct tm *mt;
int i;
time_t t;
char timestr[3];

t=time(NULL);
mt=localtime(&t);
strftime(timestr,3,"%S",mt);

srand(atoi(timestr));

}

The comp.lang.c FAQ has some advice seeding rand().
http://c-faq.com/lib/srand.html

void printlattice(int (*m)[N]){

int i,j;

/* system("clear"); */
move(0,0);

Comment this out. You don't need the curses functionality (at least
not yet). If you do more with it in future versions, it may be worth
the price of losing output re-direction.

for(i=0;i<N;i++){
putchar('\n');
for(j=0;j<N;j++){
if(m[i][j]==1)printf(" 1");
else printf(" -1");
}
}

putchar('\n');
}

void ising(int (*m)[N],double beta){

int i,j,k;
double energy,moment;
double summe,summm,summe2,summm2;
int numsteps=0;
double sum_nn,sums;
double deltaH;
double sum_nnn;
int n2=N*N;
double half=NITERS/2;

k=0;

energy=moment=0.0;
summe=summm=summe2=summm2=0.0;

// pick a site randomly

for(i=0;i<N;i++){
for(j=0;j<N;j++){
moment += m[i][j];
energy -= 2*m[i][j]*(m[(i+1)%N][j]+m[i][(j+1)%N]+m[(i+1)%N][(j
+1)%N]/5);
}
}

for(k=0;k<NITERS;k++){

i=rand()%N;
j=rand()%N;

sum_nn=m[i][((j+1)%N)]+m[i][((j-1+N)%N)]+m[((i+1)%N)][j]+m[((i-1+N)
%N)][j];
sum_nnn=(m[((i+1)%N)][((j+1)%N)]+m[((i-1+N)%N)][((j-1+N)%N)]
+m[((i-1+N)%N)][((j+1)%N)]+m[((i+1)%N)][((j-1+N)%N)])/5;
sums=sum_nn+sum_nnn;
deltaH=m[i][j]*sums;
if((exp(-1.3*deltaH*beta))>((float)rand()/(float)RAND_MAX) ||
(deltaH < 0) ){
energy += 2*deltaH;
moment -= 2*m[i][j];
m[i][j] *= -1;
}

if(k>half){
summe+=energy;
summe2+=energy*energy;
summm+=moment;
summm2+=moment*moment;
}

/* if(k>10000){
k=0;
putchar('\n');
printf("E=%f m=%f",(energy/n2),(moment/n2));
printlattice(m);
sleep(1);
} */

}

summe /= half;
summe2 /= half;
summm /= half;
summm2 /= half;

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f Chi=%5.2f\n",beta,(energy/
n2),(moment/n2),(summe2-summe*summe)/n2,(summm2-summm*summm)/n2);

Add:

fflush(stdout);

to be sure to get what data you have written so far. I did not wait for
the program to finish -- if you do there is no need to call fflush.

--
Ben.

[Ben Bacarisse]

Ben Bacarisse <be********@bsb.me.ukwrites:

curses programs can't usually have their put redirected (ask in
c.u.p for when and why).

Oh the perils of off-topic answers. Please don't get into this here.
I know it is wrong -- I was over-simplifying to the point of being
plain wrong. Berate me in comp.unix.programmer if you must!

--
Ben.

[Peter Nilsson]

[Other replies notwithstanding...]

Jordan Glassman wrote:

#define NITERS 5000000
int i,j,k;
for(k=0;k<NITERS;k++){

Are you perchance running on a machine with 16-bit ints?

If so, this loop will likely run forever (assuming 16-bit overflow
from INT_MAX to INT_MIN.)

void ising(int (*m)[N],double beta){

Identifiers starting with is (or to) and a lowercase letter are
reserved for use as external identifiers.

This is not likely to be the source of your problem, but it is
still a fault with your code.

Apart from that, the program does take some time to run.
Are you leaving it for long enough? With such relatively
small output, many systems won't actually flush to the
redirected file until the program (and stream) closes.

--
Peter

[Jordan Glassman]

Ben,

Taking out the curses.h and all associated functions did it. I'm
still not sure why the printf didn't work, though... not of the
curses.h functions were actually being used in that code I posted...
they were all commented out! It's as if curses replaces printf with
another version.

Dunno. In any case, thanks for the help.

-j

On May 12, 9:01 pm, Ben Bacarisse <[e-mail]:

Jordan Glassman <[e-mail]:

Though for some reason you decided not to post the code.
Still, your loss...

My loss? Here it is...

Yes. I can now tell you how to get it to work (but
comp.unix.programmer is still the better place).

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <curses.h>

curses programs can't usually have their put redirected (ask in
c.u.p for when and why).

#include <unistd.h// ANSI C???

No, not ANSI C.

<snip>

void seed(void){

struct tm *mt;
int i;
time_t t;
char timestr[3];

t=time(NULL);
mt=localtime(&t);
strftime(timestr,3,"%S",mt);

srand(atoi(timestr));

}

The comp.lang.c FAQ has some advice seeding rand().http://c-faq.com/lib/srand.html

void printlattice(int (*m)[N]){

int i,j;

/* system("clear"); */
move(0,0);

Comment this out. You don't need the curses functionality (at least
not yet). If you do more with it in future versions, it may be worth
the price of losing output re-direction.

for(i=0;i<N;i++){
putchar('\n');
for(j=0;j<N;j++){
if(m[i][j]==1)printf(" 1");
else printf(" -1");
}
}

putchar('\n');
}

void ising(int (*m)[N],double beta){

int i,j,k;
double energy,moment;
double summe,summm,summe2,summm2;
int numsteps=0;
double sum_nn,sums;
double deltaH;
double sum_nnn;
int n2=N*N;
double half=NITERS/2;

k=0;

energy=moment=0.0;
summe=summm=summe2=summm2=0.0;

// pick a site randomly

for(i=0;i<N;i++){
for(j=0;j<N;j++){
moment += m[i][j];
energy -= 2*m[i][j]*(m[(i+1)%N][j]+m[i][(j+1)%N]+m[(i+1)%N][(j
+1)%N]/5);
}
}

for(k=0;k<NITERS;k++){

i=rand()%N;
j=rand()%N;

sum_nn=m[i][((j+1)%N)]+m[i][((j-1+N)%N)]+m[((i+1)%N)][j]+m[((i-1+N)
%N)][j];
sum_nnn=(m[((i+1)%N)][((j+1)%N)]+m[((i-1+N)%N)][((j-1+N)%N)]
+m[((i-1+N)%N)][((j+1)%N)]+m[((i+1)%N)][((j-1+N)%N)])/5;
sums=sum_nn+sum_nnn;
deltaH=m[i][j]*sums;
if((exp(-1.3*deltaH*beta))>((float)rand()/(float)RAND_MAX) ||
(deltaH < 0) ){
energy += 2*deltaH;
moment -= 2*m[i][j];
m[i][j] *= -1;
}

if(k>half){
summe+=energy;
summe2+=energy*energy;
summm+=moment;
summm2+=moment*moment;
}

/* if(k>10000){
k=0;
putchar('\n');
printf("E=%f m=%f",(energy/n2),(moment/n2));
printlattice(m);
sleep(1);
} */

}

summe /= half;
summe2 /= half;
summm /= half;
summm2 /= half;

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f Chi=%5.2f\n",beta,(energy/
n2),(moment/n2),(summe2-summe*summe)/n2,(summm2-summm*summm)/n2);

Add:

fflush(stdout);

to be sure to get what data you have written so far. I did not wait for
the program to finish -- if you do there is no need to call fflush.

--
Ben.

[Jordan Glassman]

Ben,

Taking out the curses.h and all associated functions did it. I'm
still not sure why the printf didn't work, though... not of the
curses.h functions were actually being used in that code I posted...
they were all commented out! It's as if curses replaces printf with
another version.

Dunno. In any case, thanks for the help.

-j

On May 12, 9:01 pm, Ben Bacarisse <[e-mail]:

Jordan Glassman <[e-mail]:

Though for some reason you decided not to post the code.
Still, your loss...

My loss? Here it is...

Yes. I can now tell you how to get it to work (but
comp.unix.programmer is still the better place).

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <curses.h>

curses programs can't usually have their put redirected (ask in
c.u.p for when and why).

#include <unistd.h// ANSI C???

No, not ANSI C.

<snip>

void seed(void){

struct tm *mt;
int i;
time_t t;
char timestr[3];

t=time(NULL);
mt=localtime(&t);
strftime(timestr,3,"%S",mt);

srand(atoi(timestr));

}

The comp.lang.c FAQ has some advice seeding rand().http://c-faq.com/lib/srand.html

void printlattice(int (*m)[N]){

int i,j;

/* system("clear"); */
move(0,0);

Comment this out. You don't need the curses functionality (at least
not yet). If you do more with it in future versions, it may be worth
the price of losing output re-direction.

for(i=0;i<N;i++){
putchar('\n');
for(j=0;j<N;j++){
if(m[i][j]==1)printf(" 1");
else printf(" -1");
}
}

putchar('\n');
}

void ising(int (*m)[N],double beta){

int i,j,k;
double energy,moment;
double summe,summm,summe2,summm2;
int numsteps=0;
double sum_nn,sums;
double deltaH;
double sum_nnn;
int n2=N*N;
double half=NITERS/2;

k=0;

energy=moment=0.0;
summe=summm=summe2=summm2=0.0;

// pick a site randomly

for(i=0;i<N;i++){
for(j=0;j<N;j++){
moment += m[i][j];
energy -= 2*m[i][j]*(m[(i+1)%N][j]+m[i][(j+1)%N]+m[(i+1)%N][(j
+1)%N]/5);
}
}

for(k=0;k<NITERS;k++){

i=rand()%N;
j=rand()%N;

sum_nn=m[i][((j+1)%N)]+m[i][((j-1+N)%N)]+m[((i+1)%N)][j]+m[((i-1+N)
%N)][j];
sum_nnn=(m[((i+1)%N)][((j+1)%N)]+m[((i-1+N)%N)][((j-1+N)%N)]
+m[((i-1+N)%N)][((j+1)%N)]+m[((i+1)%N)][((j-1+N)%N)])/5;
sums=sum_nn+sum_nnn;
deltaH=m[i][j]*sums;
if((exp(-1.3*deltaH*beta))>((float)rand()/(float)RAND_MAX) ||
(deltaH < 0) ){
energy += 2*deltaH;
moment -= 2*m[i][j];
m[i][j] *= -1;
}

if(k>half){
summe+=energy;
summe2+=energy*energy;
summm+=moment;
summm2+=moment*moment;
}

/* if(k>10000){
k=0;
putchar('\n');
printf("E=%f m=%f",(energy/n2),(moment/n2));
printlattice(m);
sleep(1);
} */

}

summe /= half;
summe2 /= half;
summm /= half;
summm2 /= half;

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f Chi=%5.2f\n",beta,(energy/
n2),(moment/n2),(summe2-summe*summe)/n2,(summm2-summm*summm)/n2);

Add:

fflush(stdout);

to be sure to get what data you have written so far. I did not wait for
the program to finish -- if you do there is no need to call fflush.

--
Ben.

[Default User]

Jordan Glassman wrote:

Ben,

Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or:
<http://www.caliburn.nl/topposting.html>

[Jordan Glassman]

Please don't top-post.

Lesson learned...

[Default User]

Jordan Glassman wrote:

Please don't top-post.

Lesson learned...

Thanks!


Brian

[viza]

On May 13, 5:03 am, Richard Heathfield <[e-mail]:

Jordan Glassman said:

if((((float)rand()/(float)RAND_MAX)) 0.5)

In C, the normal way to do (pseudo) random numbers selected from N
possibilities (in the range 0 to N-1) is to get a value in the half-open
range [0, 1) like this:

rand() / (RAND_MAX + 1.0)

and then multiply by N to get a value in the half-open range [0, N).
It seems that you want a value in the half-open range [0, 1) so you can
omit the multiplication step:

if(rand() / (RAND_MAX + 1.0) 0.5)

In this case, why not just use:

if( rand() & 1 )

If RAND_MAX is odd (which it usually is) then this is perfect, and
doesn't need an FPU.

If RAND_MAX is even, then it gets very close to perfect as long as
RAND_MAX is large. Remember that the float method isn't perfect
either.

If your rand() isn't evenly distributed, then you are screwed whatever
you do.

viza

[Walter Roberson]

In article <a9**********************************@2g2000hsn.go oglegroups.com>,
viza <to******@gmail.comwrote:

>On May 13, 5:03 am, Richard Heathfield <[e-mail]:

>Jordan Glassman said:

if((((float)rand()/(float)RAND_MAX)) 0.5)

>In this case, why not just use:

>if( rand() & 1 )

>If RAND_MAX is odd (which it usually is) then this is perfect, and
doesn't need an FPU.

The low bit of rand() is often not very random at all -- often alternating
between 0 and 1 each time. It's a problem with linear congruential
pseudo-random numbers, at least if you take the bottom bits of the
new seed as being the random value. (Some implementations make sure
they never output the bottom bits to reduce this problem, but
C doesn't make any such promises.)
--
"Man's life is but a jest,
A dream, a shadow, bubble, air, a vapor at the best."
-- George Walter Thornbury

[Richard Tobin]

In article <g0**********@canopus.cc.umanitoba.ca>,
Walter Roberson <ro******@ibd.nrc-cnrc.gc.cawrote:

>The low bit of rand() is often not very random at all -- often alternating
between 0 and 1 each time.

This used to be true, 20-something years ago. Surely modern
implementations don't have the same problem?

-- Richard
--
:wq

[Walter Roberson]

In article <g0***********@pc-news.cogsci.ed.ac.uk>,
Richard Tobin <ri*****@cogsci.ed.ac.ukwrote:

>In article <g0**********@canopus.cc.umanitoba.ca>,
Walter Roberson <ro******@ibd.nrc-cnrc.gc.cawrote:

>>The low bit of rand() is often not very random at all -- often alternating
between 0 and 1 each time.

>This used to be true, 20-something years ago. Surely modern
implementations don't have the same problem?

Remember, the C89 standard was 20-something years ago, but conforming
more modern implementations (C99) are still pretty uncommon ;-)

To be fair: the C89 sample implementation works with an
unsigned long int seed, and the value returned is divided by 64K and
is mod 32768 (e.g., shift right 16 bits and mask out all but the
bottom 15 bits). With that sample algorithm, the bottom bit of rand()
should have a cycle of 64K (which would, I -suspect-, be composed
of two half-cycles of 32K each, bitwise negations of each other.)
--
"The shallow murmur, but the deep are dumb." -- Sir Walter Raleigh

[Szabolcs Borsanyi]

produces a blinking cursor, an empty file named "output," and a

program that runs forever. *With no redirect, the output is normal.

As I see your problem has been solved. I got similar behaviour
when I did not wait for the program to completely finish.
Without redirection I saw the results immediately, but
redirection sometimes implies a buffering and the buffer
is lost if the program terminates abnormally.

Below is the printf statement used to generate output.

printf("B=%4.2f E=%8.4f m=%8.4f Cv=%5.2f \
Chi=%5.2f\n",beta,(energy/n2),(moment/n2), \
(summe2-summe*summe)/n2, \
(summm2-summm*summm)/n2);

Sorry for this remark, but, this last lines made me
suspicious: This is a 2dimensional ising model,
Cv is the specific heat, which is the energy density fluctuation,
so I expect a standard deviation there.
Don't you then miss an other 1/n2 no normalise summe and summm?
I can be completely wrong, but you might want to check this.

Szabolcs