how to pass a variable from Octave to c?

Question

In the following program calculates the determinant in c via Octave. But i don´t know how to pass the variable from octave to c:

#include <stdio.h>


int main(void)
{ 
    FILE *graf;
    graf=popen("octave -persist","w");
    if (graf==NULL){
        printf("Error \n");}
    else
    { 
        int a;
 printf("input the dimension: \n");
 scanf("%d",&a);
 fprintf(graf,"N= %d;",a);
 fprintf(graf,"pkg load statistics \n");
 fprintf(graf,"M=N-1;");
 fprintf(graf," for i=1:%d \n",a);
 fprintf(graf," for j=1:%d \n",a);
 fprintf(graf," matriz(i,j)=round(1+9*rand());");
 fprintf(graf," endfor \n");
 fprintf(graf,"endfor \n");
 fprintf(graf,"C = combnk(1:%d,M);",a);
 fprintf(graf,"Combinaciones=size(C,1);");
 fprintf(graf,"for i=1:Combinaciones \n");
 fprintf(graf,"for j=1:Combinaciones \n");
 fprintf(graf,"for h=1:M \n");
 fprintf(graf,"for k=1:M \n");
 fprintf(graf,"matrices(h,k)=matriz(C(i,h),C(j,k));");
 fprintf(graf,"endfor \n");
 fprintf(graf,"endfor \n");
 fprintf(graf,"nuevamatriz(Combinaciones-i+1,Combinaciones-j+1)=det(matrices);");
 fprintf(graf,"endfor \n");
 fprintf(graf,"endfor \n");
 fprintf(graf,"matriz \n");
 fprintf(graf,"det(matriz) \n");
 fprintf(graf,"nuevamatriz \n");
 fprintf(graf,"det(nuevamatriz) \n");
pclose(graf);
    }
printf("Have that the second determinant (attached matrix) is always the first (matrix) powered at dimension less one \n\n ");
}

A way to define this determining variable in c.

@Luis Federico Berruezo Sánchez – Why do you use `-persist`? — Armali, Apr 27 '23 at 07:35
You interfacing with octave using stdio/stdout so you want to send a print variable command to octave. It looks like Alternative check out the external code interface particular the (legacy?) mex files as you are using C. — Allan Wind, Apr 27 '23 at 10:01
thank you all. But you can see that i send the variable to octave. What i don't know is receiving. — Luis Federico Berruezo Sánchez, Apr 27 '23 at 15:19
perhaps if the pipe is read-write rather than just write, and then you attempt to print from octave to stdout and then use your pipe to read from it? It "will" be just text though, not numerical. I agree with Allan, use the Mex interface if you want to perform octave operations within a c context. — Tasos Papastylianou, Apr 27 '23 at 17:57
@Luis Federico Berruezo Sánchez – Your edit doesn't answer my question. — Armali, Apr 28 '23 at 05:57

Luis Federico Berruezo Sánchez · Answer 1 · 2023-05-24T08:14:30.540

0

First: I use -persist because it's the same via to call gnuplot. Second: It motivated me to use this method was It calculating the determinant of any matrix without do so much Code. But I have solved It embedding Python in c with the header < Python.h> and compiling It like this: gcc -I/usr/include/python3.11/ program.c -lpython3.11. -o program since Python include the module numpy and It's more easy even than with octave. Thank you and here, an example:

`

#include <Python.h>
     int main() {
char a[27]="[[1,2,3],[90,23,3],[1,5,7]]";
Py_Initialize();
PyRun_SimpleString("import numpy as np");
PyRun_SimpleString("det=np.linalg.det([[1,2,3],[90,23,3],
[1,5,7]])");
PyRun_SimpleString("print('the determinant is:',det)");
Py_Finalize();
return 0;
}`

edited May 24 '23 at 08:14

answered May 16 '23 at 14:26

Luis Federico Berruezo Sánchez

11
2

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community May 16 '23 at 15:14
You can do exactly the same thing with Octave, see linked duplicate or the [documentation](https://docs.octave.org/v8.2.0/Standalone-Programs.html#Standalone-Programs). – Cris Luengo May 24 '23 at 14:15

score 0 · Answer 2 · answered May 24 '23 at 07:57

it can also be done as follows,so the variable is stored in a file and then it can be recovered. This program reads an square matrix like a list of numbers starting with a number that is the dimension from a file, after save the determinant in another file. I use it to compare matrices and determinants.

#include <stdio.h>
void enteroACadena(int numero, char *bufer);
int main(void)
{
char file[10];
printf("Enter the name of the file: \n");
scanf("%s",file);
FILE *fp;
 FILE *graf;
 graf=popen("octave","w");
 fprintf(graf,"clear; \n");
int buffer[50][50];
int g;
fp = fopen ( file, "r" );
fscanf(fp, "%d", &g);
for(int r1=1;r1<g+1;r1++)
{
for(int r2=1;r2<g+1;r2++)
{
fscanf(fp, "%d" ,&buffer[r1][r2]);
char cadena[11]; // 
    char cadena1[3];
    char cadena2[3];
    enteroACadena(buffer[r1][r2], cadena);
    enteroACadena(r1, cadena1);
    enteroACadena(r2, cadena2);
fprintf(graf,"matriz(%s,%s)=%s;\n",cadena1,cadena2,cadena);
//printf("matriz(%s,%s)=%s;  ",cadena1,cadena2,cadena);
}
    printf("\n");
    }

 fprintf(graf,"d=det(matriz) \n");
 fprintf(graf,"save %s.det d \n",file);
pclose(graf);

fclose ( fp );

return 0;
}
void enteroACadena(int numero, char *bufer){

    sprintf(bufer, "%d", numero);
}

how to pass a variable from Octave to c?

2 Answers2