Can a function returns a matrix?

[Balaji.V]

hi all,
I want a function that takes matrix as input and returns a
matrix. (say, function that performs matrix multiplication) . How can I
go about this? Can anybody help me?
Balaji.V

[MQ]

Balaji.V wrote:

hi all,
I want a function that takes matrix as input and returns a
matrix. (say, function that performs matrix multiplication) . How can I
go about this? Can anybody help me?
Balaji.V

Define a matrix data structure. Pass a pointer to the structure to the
function. There are probably already matrix algebra implementations in
the standard library, so take a look...

MQ

[Keith Thompson]

"MQ" <mi************ **@gmail.comwri tes:

Balaji.V wrote:

> I want a function that takes matrix as input and returns a
matrix. (say, function that performs matrix multiplication) . How can I
go about this? Can anybody help me?

Define a matrix data structure. Pass a pointer to the structure to the
function. There are probably already matrix algebra implementations in
the standard library, so take a look...

There are no matrix algebra functions in the C standard library.
There probably are such functions in third-party libraries (the
details of which are off-topic here).

There's no one way to represent a matrix; if you're going to use one
of these libraries, you'll have to conform to the representation it
expects.

If you want to roll your own, section 6 of the FAQ,
<http://www.c-faq.com/>, has some good information on allocating
multidimensiona l arrays.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Bernard Xhumga]

You can try my work, I give an example.

Windows : Dev-C++ 4
Linux : gcc abc.c -lm Return
a.out Return

First step :
http://www.geocities.com/xhungab/tutorial/t04a.zip

Second step :
http://www.geocities.com/xhungab/tutorial/t04b.zip

Example

/* http://groups.yahoo.com/group/mathc/ */
/* ------------------------------------------ */
#include <stdio.h /* getchar(); */

/*-------------------------- Matrix structure */
typedef struct
{
int rows;
int cols;
double *pb; /* Pointer on a block of memory */
} mR, /* Type mR */
*PmR; /* Pointer on a type mR */

/* --------------------------------- FUNCTION */
/* Do : create a matrix without initialization. */
/* ------------------------------------------- */
double * create_mR(
int r, /* (r)ow */
int c /* (c)olumn */
)
{
double *P_A;

P_A = (double *) malloc(r*c*size of(double));

if(P_A==NULL){e xit(1);}

return(P_A);
}

/* --------------------------------- FUNCTION */
/* Do : print matrix A. */
/* ---------------------------------------- - */
void p_mR(
PmR A /* matrix A */
)
{
int r; /* (r)ow */
int c; /* (c)olumn */

for(r=0 ; r<A->rows; r++)
{
printf("\n");
for(c=0 ;c<A->cols ;c++)
printf(" %+8.3f",*(A->pb+r *A->cols+c));
}
printf("\n");
}

/* --------------------------------- FUNCTION */
/* Do : copy A into B. */
/* ---------------------------------------- - */
void copy_mR(
PmR A,
PmR B)
{
int r; /* (r)ow */
int c; /* (c)olumn */

for ( r=0; r<A->rows; r++)
for ( c=0; c<A->cols; c++)

*(B->pb+r *B->cols+c) = *(A->pb+r *A->cols+c);
}

/* --------------------------------- MAIN */
int main(void)
{
double pbA[3][2]=
{
1, 2,
3, 4,
5, 6,
};mR A={3,2,&pbA[0][0]};

mR B ={3,2,create_mR (3,2)}; /* malloc */
/*-------------------------------- PROGRAM */
printf("\nMatri x A :\n");
p_mR(&A);

copy_mR(&A,&B);

printf("\nMatri x B :\n");
p_mR(&B);

free( B.pb);

printf("\n Press Return to continue");
getchar();
return 0;
}

[Flash Gordon]

Bernard Xhumga wrote:

You can try my work, I give an example.

Windows : Dev-C++ 4
Linux : gcc abc.c -lm Return
a.out Return

First step :
http://www.geocities.com/xhungab/tutorial/t04a.zip

Second step :
http://www.geocities.com/xhungab/tutorial/t04b.zip

Example

/* http://groups.yahoo.com/group/mathc/ */
/* ------------------------------------------ */
#include <stdio.h /* getchar(); */

/*-------------------------- Matrix structure */
typedef struct
{
int rows;
int cols;
double *pb; /* Pointer on a block of memory */
} mR, /* Type mR */
*PmR; /* Pointer on a type mR */

/* --------------------------------- FUNCTION */
/* Do : create a matrix without initialization. */
/* ------------------------------------------- */
double * create_mR(
int r, /* (r)ow */
int c /* (c)olumn */
)
{
double *P_A;

P_A = (double *) malloc(r*c*size of(double));

<snip>

No need to go further than this before saying DO NOT use this code.
Calling malloc without a valid prototype in scope invokes undefined
behaviour and it DOES cause problem on real MODERN systems. Casting the
return value shuts up the compiler but it does NOT solve the problem.

Search this group and read the comp.lang.c FAQ for further information.
--
Flash Gordon
Still sigless on this computer

[Bernard Xhumga]

What do you think of this code.

thank.

/* .c freeware
http://groups.yahoo.com/group/mathc/ */
/* -------------------------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
/* ------------------------------- FUNCTION */
/* Do : print matrix A. */
/* ---------------------------------------------- */
void p_mR(
double **A,
int r,
int c
)
{
int i;
int j;

for (i=0; i<r; i++)
{
for (j=0; j<c; j++)printf(" %+6.2f ",A[i][j]);
printf("\n");
}
}

/* ------------------------------- FUNCTION */
/* Do : copy A -B. */
/* ---------------------------------------------- */
void c_mR(
double **A, /* matrix A */
double **B, /* matrix B */
int r,
int c
)
{
int i;
int j;

for (i=0; i<r; i++)
for (j=0; j<c; j++) B[i][j] = A[i][j];
}

/* --------------------------------- MAIN */
int main()
{
int i;
int j;
int n;
int r=4;
int c=4;

double **A = malloc(r * sizeof( *A) );
double **B = malloc(r * sizeof( *B) );

/*------------------------- INITIALISATION */

A[0] = malloc(r * c * sizeof(**A) );
for(i=1; i<r; i++) A[i] = A[0]+i*c;

B[0] = malloc(r * c * sizeof(**B) );
for(i=1; i<r; i++) B[i] = B[0]+i*c;

/*-------------------------------- PROGRAM */

for (i=0,n=0; i<r; i++)
for (j=0; j<c; j++) A[i][j]=n++;

printf(" A : \n");
p_mR(A,r,c);
printf("\n");
c_mR(A,B,r,c);
printf(" B : \n");
p_mR(B,r,c);

printf("\n Press Return to continue");
getchar();

return 0;
}

[Richard Heathfield]

Bernard Xhumga said:

What do you think of this code.

I think it fails to handle the possibility that memory resource requests can
fail.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Bernard Xhumga]

Perhaps this time it is good.

/* http://groups.yahoo.com/group/mathc/ */
/* ---------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
/* --------------------------------- FUNCTION */
/* Do : print matrix A. */
/* ---------------------------------------------- */
void p_mR(
double **A,
int r,
int c
)
{
int i;
int j;

for (i=0; i<r; i++)
{
for (j=0; j<c; j++)printf(" %+6.2f ",A[i][j]);
printf("\n");
}
}

/* --------------------------------- FUNCTION */
/* Do : copy A -B. */
/* ------------------------------------------------ */
void c_mR(
double **A,
double **B,
int r,
int c
)
{
int i;
int j;

for (i=0; i<r; i++)
for (j=0; j<c; j++) B[i][j] = A[i][j];
}

/* --------------------------------- FUNCTION */
/* Do : initialize a matrix A. */
/* ------------------------------------------------ */
double **i_mR(
int r,
int c
)
{
int i;

double **A = malloc(r * sizeof( *A) );
if(!A){exit(1); }

A[0] = malloc(r * c * sizeof(**A) );
if(!A[0]){exit(1);}

for(i=1; i<r; i++)
{
A[i] = A[0]+i*c;
if(!A[i]){exit(1);}
}

return(A);
}

/* --------------------------------- FUNCTION */
/* Do : */
/* ------------------------------------------------ */
void f_mR(
double **A,
int r
)
{
int i;
int j;

for(i=0; i<r; i++) free((void *)A[i]);

free((void *)A);
}
/* --------------------------------- MAIN */
int main()
{
int i;
int j;
int n;
int r;
int c;

double **A;
double **B;
/*------------------------- INITIALISATION */
r = 7;
c = 9;

A = i_mR(r,c);
B = i_mR(r,c);
/*-------------------------------- PROGRAM */

for (i=0,n=0; i<r; i++)
for (j=0; j<c; j++) A[i][j]=n++;

printf(" A : \n");
p_mR(A,r,c);
printf("\n");
c_mR(A,B,r,c);
printf(" B : \n");
p_mR(B,r,c);

f_mR(A,r);
f_mR(B,r);

printf("\n Press Return to continue");
getchar();

return 0;
}

[Flash Gordon]

Bernard Xhumga wrote:

Perhaps this time it is good.

No. It is still obviously flawed.

<snip>

/* --------------------------------- FUNCTION */
/* Do : initialize a matrix A. */
/* ------------------------------------------------ */
double **i_mR(
int r,
int c
)
{
int i;

double **A = malloc(r * sizeof( *A) );
if(!A){exit(1); }

A[0] = malloc(r * c * sizeof(**A) );
if(!A[0]){exit(1);}

Two calls to malloc.

for(i=1; i<r; i++)
{
A[i] = A[0]+i*c;
if(!A[i]){exit(1);}
}

return(A);
}

/* --------------------------------- FUNCTION */
/* Do : */
/* ------------------------------------------------ */
void f_mR(
double **A,
int r
)
{
int i;
int j;

for(i=0; i<r; i++) free((void *)A[i]);

free((void *)A);

r+1 calls to free.

}

<snip>

int main()

Better to be explicit about not using parameters.
int main(void)

{

<snip>

printf("\n Press Return to continue");

There is no guarantee the message will be printed before waiting for
input. To stand a better chance of the message being seen

fflush(stdout);

getchar();

return 0;
}

There is also an unused variable, in my opinion this is a sign of sloppy
programming.
--
Flash Gordon
Still sigless on this computer

[Bernard Xhumga]

Now it is perfect ?

Perhaps

/* .c freeware
http://groups.yahoo.com/group/mathc/ */
/* -------------------------------------------------------------------------
- */
#include <stdio.h>
#include <stdlib.h>
/* --------------------------------- FUNCTION */
/* Do : initialize a matrix A. */
/* ----------------------------------------------- */
double **i_mR(
int r,
int c
)
{
int i;

double **A = malloc(r * sizeof( *A) );
if(!A)exit(1);

A[0] = malloc(r * c * sizeof(**A) );
if(!A[0])exit(1);

for(i=1; i<r; i++)
{
A[i] = A[0]+i*c;
if(!A[i])exit(1);
}

return(A);
}
/* --------------------------------- FUNCTION */
/* Do : */
/* ----------------------------------------------- */
void f_mR(
double **A
)
{
free((void *)A[0]);
free((void *)A);
}
/* --------------------------------- MAIN */
int main(void)
{
int r;
int c;

double **A;
double **B;
/*------------------------- INITIALISATION */
r = 7;
c = 9;

A = i_mR(r,c);
B = i_mR(r,c);
/*-------------------------------- PROGRAM */

f_mR(A);
f_mR(B);

printf("\n Press Return to continue");
fflush(stdout);
getchar();

return 0;
}