Fortran Program - Calculate the Function

[Haleemos]

Homework Statement

F(x) = exp(-a x^2) cos bx
for -100 =< x >= 100 , a=13 and b=7.

Homework Equations

...

The Attempt at a Solution

program main

implicit double precision (A-H,O-Z)
implicit integer (I-N)

DO I = -100,100
X = I * 1D0

F = DEXP(-A * X**2) * DCOS(B * X)

A = 13
B = 7

PRINT*,F
ENDDO

STOP
END

 

[DrClaude]

Have you tested the program to see if it works?

Because it will not give the right result. Check the order in which you are doing things.

 

[Haleemos]

the program works

but the answers all zero

 

[DrClaude]

but the answers all zero

Are you sure about that? Because it is not the case when I run it.

You only made one mistake, which is that a and b are set too late. And they shouldn't be inside the loop: set them at the beginning of the program. Might as well also set them directly as double precision

a = 13.d0
b = 7.d0

Also, instead of multiplying by 1D0, set I to double precision using

X = dble(I)

This is more efficient as there will not be an unnecessary multiplication every time.

I also suggest that you print out both x and F, which makes it easier to check the output and plot the results.

 

[rezeew]

I would first commend the use of Fortran for this calculation, as it is a powerful and efficient language for scientific computing. The program provided seems to be a straightforward implementation of the given function, with appropriate use of implicit declarations and a loop to evaluate the function for a range of values.

One suggestion for improvement would be to add comments or documentation to the code to make it easier for others to understand and potentially modify in the future. Additionally, it may be useful to add some error handling in case the input values for a and b are not appropriate.

Overall, this is a solid program for calculating the given function and can be easily modified for other similar calculations.