Converting Matlab code to C code

AW
2012 2 29
6 个回答
4 次查看（30 天）

0 个投票

I'm trying to convert the following matlab code to c code, I did it both in windows and in linux systems by using Visual Studio in windows and gcc in linux as the compiler. However I couldn't get correct results by running the generated c code. Can anyone have a idea how to modify this matlab code in order to generate the matched c code? I would appreciate that!
function matc(n)
val = 0;
for i = 1:n
x = 2*rand(3,1);
val = val + f(x);
end
val = 2^3*val/n

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AW
AW 2012-2-29
function y = f(x)
y = sin(x(1) + x(2)^2 +x(3)^3);
James Tursa
James Tursa 2012-2-29
Please format your code so it is readable. Is the function supposed to return val? Are you looking for a mex function, or just a C-language code snippet?
AW
AW 2012-2-29
Right, return val. I was trying to generate a c executable by initializing n with a value(for example, adding n=1000 to the code). Thanks.
function matc(n)
val = 0;
for i = 1:n
x = 2*rand(3,1);
val = val + f(x);
end
val = 2^3*val/n
function y = f(x)
y = sin(x(1) + x(2)^2 +x(3)^3);
Kaustubha Govind
Kaustubha Govind 2012-2-29
How exactly do the results vary?
AW
AW 2012-2-29
Sometimes I got val=4.94066e-324, sometimes I got val=0. I use the following code in file main.c:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "matc.h"
int main()
{
printf("matc=%g\n", matc());
return 0;
}
I'm not sure if it's because of the main.c file, I have modified it to several different versions, but still couldn't get the matched c code.
Any idea? Thanks for your help!

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回答（6 个）

Kaustubha Govind
Kaustubha Govind 2012-3-1

2 个投票

To expand's on Walter's answer, your MATLAB code should look like this:
function val = matc(n)
val = 0;
for i = 1:n
x = 2*rand(3,1);
val = val + f(x);
end
val = 2^3*val/n
function y = f(x)
y = sin(x(1) + x(2)^2 +x(3)^3);
(Note how 'val' is being returned from the function by adding it to the "function" line).
And your C code should look like this:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "matc.h"
int main()
{
printf("matc=%g\n", matc(0.2));
return 0;
}
Note how an input value needs to be passed into matc.
Walter Roberson
Walter Roberson 2012-2-29

0 个投票

You are not passing any value from the C code to the matc() routine. The initial value of an undefined parameter is undefined, so any result could occur.
AW
AW 2012-2-29

0 个投票

Thanks for your replying. I defined n as double(1x1) while I was creating a project using matlab coder. Is that fine?

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Walter Roberson
Walter Roberson 2012-2-29
Yes, having it declared as type double is fine, but you still need to pass a specific variable in to matc() when you make the call to matc()
printf("matc=%g\n", matc(42.));

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AW
AW 2012-3-1

0 个投票

Thanks a lot! I tested it with your suggestions, still get a result of 0. I use the following command for generating c code, codegen -config cfg matc -args {1000}

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Walter Roberson
Walter Roberson 2012-3-1
What does your code look like at present?
AW
AW 2012-3-1
function val = matc(n) %#codegen
val = 0;
for i = 1:n
x = 2*rand(3,1);
val = val + f(x);
end
val = 2^3*val/n
function y = f(x)
y = sin(x(1) + x(2)^2 +x(3)^3);
in file main.c,
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "matc.h"
int main()
{
printf("matc=%g\n", matc(1000));
return 0;
}
Walter Roberson
Walter Roberson 2012-3-1
Looks plausible. I would put a line in matc() displaying the value of n at the beginning, to cross-check that you are getting the input you expect.
AW
AW 2012-3-2
Thank you for the suggestion. I did it with adding n=1000, but still got a 0.
Kaustubha Govind
Kaustubha Govind 2012-3-2
Try putting a statement "disp(val)" at the bottom of your "matc" function and recompile the code. Does the MATLAB code display a zero too?
AW
AW 2012-3-2
I got an error message shows that "Function 'disp' is not supported for code generation. Consider using coder.extrinsic('disp') to bypass code generation.". So I added "coder.extrinsic('disp')" associated with "disp(val)". But still get a zero.
Walter Roberson
Walter Roberson 2012-3-2
So somehow the argument isn't getting passed in correctly, I don't know why at the moment.
Say, what does matc.h contain?
AW
AW 2012-3-2
/*
* matc.h
*/
#ifndef __MATC_H__
#define __MATC_H__
/* Include files */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "rt_nonfinite.h"
#include "rtwtypes.h"
#include "matc_types.h"
/* Type Definitions */
/* Named Constants */
/* Variable Declarations */
/* Variable Definitions */
/* Function Declarations */
extern real_T matc(real_T n);
extern void matc_initialize(void);
extern void matc_terminate(void);
#endif
Walter Roberson
Walter Roberson 2012-3-2
Hmmm, I wonder if real_T is single or double precision?
And I wonder if the code generator is treating 1000 as integer?
Could I ask you to indulge my curiosity and try 1000. (with the perod to force syntactic floating point) ? And to also try with
single(1000) and double(1000) ?
AW
AW 2012-3-2
I did the tests with 1000., single(1000) and double(1000). All come with zero results.

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AW
AW 2012-3-7

0 个投票

Anyone has an idea? Thanks.

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Kaustubha Govind
Kaustubha Govind 2012-3-8
AW: I would recommend using a "disp" command in your script. Since disp is not supported for code-generation, you need to add this line at the top of your function:
coder.extrinsic('disp');
%eml.extrinsic('disp') for older versions of MATLAB
Then, generate a MEX-file from your code (instead of standalone C code). You can use the command:
>> codegen -config:mex matc.m
Then run the generated MEX-file in MATLAB. What does the disp command show?

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AW
AW 2012-3-21

0 个投票

Thanks all for your suggestions!
Finally the code was generated to C successfully. Updated matc.m and main.c are listed as following.
% matc.m
function val = matc(n) %#codegen
val = 0;
for i = 1:n
x = 2*rand(3,1);
val = val + f(x);
end
val = 2^3*val/n;
end
function y = f(x)
y = sin(x(1) + x(2)^2 +x(3)^3);
end
------------------------------------------
/*
** main.c
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "matc.h"
#include "matc_initialize.h"
#include "matc_terminate.h"
int main()
{
matc_initialize();
printf("matc=%lf\n", matc(1000));
matc_terminate();
return 0;
}

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Kaustubha Govind
Kaustubha Govind 2012-3-22
Thanks for posting back your answer, AW. So what exactly was the error you were making before?
Walter Roberson
Walter Roberson 2012-3-22
The difference seems to be the %#codegen

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AW
2012-2-29

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