I want to compile sample c code from Rosettacode. I want to adapt it from my iOS project to do a simple matrix multiply where one of the 2 matrices is just a row, not a row and a column. The Rosettacode is as follows.
#include <stdio.h>
#include <stdlib.h>
/* Make the data structure self-contained. Element at row i and col j
is x[i * w + j]. More often than not, though, you might want
to represent a matrix some other way */
typedef struct { int h, w; double *x;} matrix_t, *matrix;
inline double dot(double *a, double *b, int len, int step)
{
double r = 0;
while (len--) {
r += *a++ * *b;
b += step;
}
return r;
}
matrix mat_new(int h, int w)
{
matrix r = malloc(sizeof(matrix) + sizeof(double) * w * h);
r->h = h, r->w = w;
r->x = (double*)(r + 1);
return r;
}
matrix mat_mul(matrix a, matrix b)
{
matrix r;
double *p, *pa;
int i, j;
if (a->w != b->h) return 0;
r = mat_new(a->h, b->w);
p = r->x;
for (pa = a->x, i = 0; i < a->h; i++, pa += a->w)
for (j = 0; j < b->w; j++)
*p++ = dot(pa, b->x + j, a->w, b->w);
return r;
}
void mat_show(matrix a)
{
int i, j;
double *p = a->x;
for (i = 0; i < a->h; i++, putchar('\n'))
for (j = 0; j < a->w; j++)
printf("\t%7.3f", *p++);
putchar('\n');
}
int main()
{
double da[] = { 1, 1, 1, 1,
2, 4, 8, 16,
3, 9, 27, 81,
4,16, 64, 256 };
double db[] = { 4.0, -3.0, 4.0/3,
-13.0/3, 19.0/4, -7.0/3,
3.0/2, -2.0, 7.0/6,
-1.0/6, 1.0/4, -1.0/6};
matrix_t a = { 4, 4, da }, b = { 4, 3, db };
matrix c = mat_mul(&a, &b);
/* mat_show(&a), mat_show(&b); */
mat_show(c);
/* free(c) */
return 0;
}
I have found some pointers here but I am getting compile errors and need more guidance.
The xcode 4.5.2 project is currently for a Mac, but ultimately will be part of a project for iOS.
The compile errors I get are as follows.
Undefined symbols for architecture x86_64:
"_dot", referenced from:
_mat_mul in code.o
ld: symbol(s) not found for architecture x86_64
I have placed the code in a file named code.m which has its own function main() and I wonder if that conflicts with the file main.m's main() function, for example?
Also, I would like to know how to actually see the resulting demo which I suppose requires using NSLog in the code.
Btw, in the array db[], what does the data notation using / mean? Does it signify a rational fraction?
