I need help with Taylor Series
Part A:
Scan the angle in degrees x_deg. Express this angle in
radians by using x=PI*x_deg/180, and calculate Y=cos^2(x)
by using the math.h library of functions (pow() and cos()
functions). Compare the so calculated value of Y=cos^2(x)
with the approximate value y obtained by using n_term
terms of the Taylor series
cos^2(x)=0.5*(1+Sum[(-1)^n (2*x)^(2n)/(2n)!]),
where n goes from 0 to n_term. Print the relative error
100*(Y-y)/Y.
Scan an integer value of n_term. Evaluate (2n)! by an embedded
for-loop statement. Use two do/while statements to continue
the calculations for different n_term and different x_deg. For
example, use flag=1 to continue calculations for different n_term
within the inner do/while loop, and flag=0 to exit that loop.
Use Flag=1 to continue calculations for different x_deg
within the outer do/while loop, and Flag=0 to exit that loop
and go to Part B. (Recall that 0!=1).
This is my program:
#include <stdio.h>
#include <math.h>
#define PI 3.141592654
main()
{
int n_terms, n=0;
double angle_deg, angle_rad, csa, csa2, taylor, sum;
printf("\n\nPart A:\nCalculation of True and Approximate Values of cos^2(x)\n\n");
printf("Enter x_deg: \n");
scanf("%lf", &angle_deg);
angle_rad = angle_deg * (PI/180.);
csa = cos(angle_rad);
csa2 = pow(csa, 2.);
printf("True value of cos^2(x) = %f\n\n", csa2);
printf("n_term approximation of cos^2(x)\n\n");
printf("Enter number of terms:\n");
scanf("%d", &n_terms);
printf("\n%d term approximation\n", n_terms);
}
so far everything shows up correctly. I'm just stuck on how to use the for loop to calculate the taylor series.
12 39100 Banfa 9,065
Expert Mod 8TB
The pseudo code to calculate the value of any series goes something like this -
INITIALISE SERIES VALUE
-
-
FOR EACH TERM IN THE SERIES
-
SERIES VALUE = SERIES VALUE + VALUE OF TERM
-
END FOR
-
-
OUTPUT SERIES VALUE
-
sorry, i'm new to programming
could you give like a simple example of how to do it? how many double / float values would i need to define?
Banfa 9,065
Expert Mod 8TB
A minimum of 1 double value to hold the total and 2 integer values, 1 to hold the current term number and 1 to hold the number of terms to evaluate. You may need more for complex terms or to make the calculation more readable.
so taking ** to mean to the power of (e.g. 3 ** 2 = 9) to evaluate the series
1 / (2**0) + 1 / (2**1) + 1 / (2**2) + 1 / (2**3) + 1 / (2**4) + ... + 1 / (2**n)
i.e. the some of recipricals of the powers of 2 (this tends to the value 2)
the code could look something like -
#include <stdio.h> /* For the pow function */
-
#include <math.h> /* For the pow function */
-
-
int main()
-
{
-
double value;
-
int term;
-
int number_of_terms = 10; /* Note I have arbitarily chose this value for this case */
-
-
value = 0.0; /* Initialise series value */
-
-
/* For each term required */
-
for( term=0; term<number_of_terms; term++)
-
{
-
value += 1.0 / pow(2.0, term); /* Add the value of this term to the total */
-
}
-
-
printf( "The sum of the recipricol of the powers of 2 to %d terms is %f\n",
-
number_of_terms,
-
value);
-
return 0;
-
}
okay thanks
i'll see if that works and update if it does or not =]
okay, i tried to do what you said. this is the code i came up with.
#include <stdio.h>
#include <math.h>
#define PI 3.141592654
main()
{
int n_terms, n=0;
double angle_deg, angle_rad, csa, csa2, value;
printf("\n\nPart A:\nCalculation of True and Approximate Values of cos^2(x)\n\n"
);
printf("Enter x_deg: \n");
scanf("%lf", &angle_deg);
angle_rad = angle_deg * (PI/180.);
csa = cos(angle_rad);
csa2 = pow(csa, 2.);
printf("True value of cos^2(x) = %f\n\n", csa2);
printf("n_term approximation of cos^2(x)\n\n");
printf("Enter number of terms:\n");
scanf("%d", &n_terms);
printf("\n%d term approximation\n", n_terms);
for(n=0; n<n_terms; n++){
value += 0.5 * 1 + (pow(-1.0, n) * pow((2 * angle_rad), (2 * n)) / (2 * n));
}
printf("cos^2(x) = %g", value);
}
is there a definition in C programming that lets me do factorials? because when i defined the value...i need the last (2 * n) to be (2 * n)!.
thanks
This is my program so far. I got the factorial to work.
#include <stdio.h>
#include <math.h>
#define PI 3.141592654
main()
{
int n_terms, n=0;
double angle_deg, angle_rad, csa, csa2, value, sum, factorial;
printf("\n\nPart A:\nCalculation of True and Approximate Values of cos^2(x)\n\n");
printf("Enter x_deg: \n");
scanf("%lf", &angle_deg);
angle_rad = angle_deg * (PI/180.);
csa = cos(angle_rad);
csa2 = pow(csa, 2.);
printf("True value of cos^2(x) = %f\n\n", csa2);
printf("n_term approximation of cos^2(x)\n\n");
printf("Enter number of terms:\n");
scanf("%d", &n_terms);
printf("\n%d term approximation\n", n_terms);
for(n=0; n<n_terms; n++){
value = 0.5 * (1 + sum);
sum += (pow(-1.0, n_terms) * (pow((2. * angle_rad), (2. * n_terms))/ factorial));
factorial += (2 * (n_terms - n));
}
printf("cos^2(x) = %g\n", value);
}
however, the value for the taylor series will not come out correctly. anyone have any suggestions. this is what the taylor series should be.
cos^2(x)=0.5*(1+Sum[(-1)^n (2*x)^(2n)/(2n)!])
Banfa 9,065
Expert Mod 8TB
You never initialise the value factorial
but what if there is no math.h
can you still make a program converting the sine of a number using taylor series?
how? pls help thnx..
Banfa 9,065
Expert Mod 8TB
but what if there is no math.h
can you still make a program converting the sine of a number using taylor series?
how? pls help thnx..
Why would there be no math.h?
can nyou try it using the taylor series?
Why would there be no math.h?
using this format:
in getting the sin of a value x:
sin(x) = x^1/1! - x^3/3! + x^5/5!....
You do know that is a Taylor series, right? Whether or not <math.h> is there has no effect on that...and <math.h> is a standard library. It should always be there, unless you're on a microcontroller or something. Note that if you're using gcc, you need to compile with the -lm flag to actually have the math library included, as well as the #include.
Thread necromancy aside, you'd just need to write your own exponent function to replace pow(), as that's the only math.h function involved in the computations.
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