71 lines
1.2 KiB
C++
71 lines
1.2 KiB
C++
// Cofactor of a matrix component.
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#include "stdafx.h"
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#include "defs.h"
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void
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eval_cofactor(void)
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{
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int i, j, n;
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push(cadr(p1));
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eval();
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p2 = pop();
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if (istensor(p2) && p2->u.tensor->ndim == 2 && p2->u.tensor->dim[0] == p2->u.tensor->dim[1])
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;
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else
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stop("cofactor: 1st arg: square matrix expected");
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n = p2->u.tensor->dim[0];
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push(caddr(p1));
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eval();
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i = pop_integer();
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if (i < 1 || i > n)
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stop("cofactor: 2nd arg: row index expected");
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push(cadddr(p1));
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eval();
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j = pop_integer();
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if (j < 1 || j > n)
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stop("cofactor: 3rd arg: column index expected");
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cofactor(p2, n, i - 1, j - 1);
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}
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void
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cofactor(U *p, int n, int row, int col)
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{
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int i, j;
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for (i = 0; i < n; i++)
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for (j = 0; j < n; j++)
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if (i != row && j != col)
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push(p->u.tensor->elem[n * i + j]);
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determinant(n - 1);
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if ((row + col) % 2)
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negate();
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}
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#if SELFTEST
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static char *s[] = {
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"cofactor(((1,2),(3,4)),1,1)",
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"4",
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"cofactor(((1,2),(3,4)),1,2)",
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"-3",
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"cofactor(((1,2),(3,4)),2,1)",
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"-2",
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"cofactor(((1,2),(3,4)),2,2)",
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"1",
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"cofactor(((1,2,3),(4,5,6),(7,8,9)),1,2)",
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"6",
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};
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void
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test_cofactor(void)
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{
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test(__FILE__, s, sizeof s / sizeof (char *));
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}
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#endif
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