如何挂钩MATLAB以评估C代码中的符号衍生物？

Question

如何使用MATLAB的符号工具包来象征性地评估C或C++的衍生物？

Answer 1

下面是一个工作示例，其中包含C以及用于gcc \ Linux的Makefile。如果任何人都可以提供Windows或Mac的构建说明，请执行。

首先C代码：

#define _GNU_SOURCE 
#include <stdio.h> 
#include <ctype.h> 
#include <stdlib.h> 
#include <string.h> 
#include <engine.h> 

int main (int argc, char *argv[]) 
{ 
    Engine *engine; 
    mxArray *f; 
    mxChar *output; 
    char  *input; 
    char  *command; 
    size_t  input_size; 
    int  i; 

    engine = engOpen ("matlab -nojvm"); 
    engEvalString (engine, "syms x"); 

    input = NULL; 
    printf (">> "); getline (&input, &input_size, stdin); 
    while (!feof (stdin)) { 
     // remove the \n character 
     input[strlen (input) - 1] = '\0'; 
     command = (char *)malloc (strlen (input) + 19); 
     sprintf (command, "f=simple(diff(%s,x))", input); 

     // execute the `diff` command on the user input expression 
     engEvalString (engine, command); 

     // the MATLAB engine does not understand the Symbolic Toolbox 
     // therefore you have to convert the output expression into 
     // some textual form (ccode,fortran,matlabFunction,latex) 
     engEvalString (engine, "fstr=ccode(f)"); 
     f = engGetVariable (engine, "fstr"); 
     output = mxGetChars (f); 

     // the expression is prefixed with some left-hand line (eg, "t0=") 
     // so, discard everything to the left of the =, and display just 
     // the derivative 
     for (i = 0; output[i] != '='; i++); 
     i++; // skip the = 

     // `mxChar` is a 16-bit character, and `printf ("%ls")` is giving 
     // me errors, so go through the string one character at a time, until 
     // the semicolon is found (it is C-code), ignoring non-printable 
     // characters along the way. 
     for (; output[i] != ';'; i++) { 
      if (isgraph (output[i])) { 
       putchar (output[i]); 
      } 
     } 
     putchar ('\n'); 
     printf (">> "); getline (&input, &input_size, stdin); 
    } 

    printf ("exiting...\n"); 
    engClose (engine); 
    return EXIT_SUCCESS; 
} 

如果你需要使用的表达，而不是仅仅呼应它，你将不得不写自己的解析器。但是由于它是一个简单的C表达式（使用math.h函数），它是相当平凡的。

这里是我的Makefile，没有什么奇特的..只记得适当地设置你的路径。

CC=gcc 
CFLAGS=-O0 -g -Wall -I$(MATLAB_DIR)/extern/include 
LDFLAGS=-L$(MATLAB_DIR)/bin/glnxa64 -leng -lmx -lmat -lut -licudata -licuuc -licui18n -licuio -lhdf5 
MATLAB_DIR=/opt/matlab/2008a 

%.o: %.c 
    $(CC) $(CFLAGS) -c $< -o [email protected] 

diff_test: diff_test.o 
    $(CC) $< -o [email protected] $(LDFLAGS) 

最后一个快速演示：

# ./diff_test 
>> sin(x) 
cos(x) 
>> 2*x^2*tan(x) 
2.0*x*(2.0*tan(x)+x+x*pow(tan(x),2.0)) 
>> log(x^2) 
2.0/x 
>> ^D 
exiting...