3 replies to this topic

[rogan2915]

Hi all,

I'm writing a program that multiplies a vector by a constant matrix, and then adds a constant vector to that result. The vector is then normalized, and the process continues.

Unfortunately, my program runs but I'm not seeing the correct results. Here's the code:

#include <stdio.h>

#include <math.h>

double unit_norm(double x[4], int cols);

void matrix_mult(double K[4][4], double x[4], double y[4], int rows);

main()

{

int rows = 4, cols = 4, k, rep = 0;

double K[4][4] = { { 2., -4.,  0.,  1.},

                   {-4.,  5., -2.,  1.},

                   { 1., -1.,  6., -3.},

                   { 0.,  2., -3.,  7.}};

double x[4] = { 1./3, 2./3, -1./3, pow(3.,0.5)/3.};

double a[4] = { 1./4., -1./2, 3./4, sqrt(2.)/.4};

double y[4] = { 0, 0, 0, 0};

printf("\nInitial vector:\n");

printf("x[%d] = [ ", rep);

for (k=0; k<rows; k++) printf("%f   ",x[k]);

printf("]\n\n");

for (rep=1; rep<8; rep++)

{

matrix_mult(K, x, y, rows);

for (k=0; k<rows; k++) x[k]=a[k]+y[k];

k=0;

for (k=0; k<rows; k++) y[k]=0;

k=0;

printf("New vector:\n");

printf("x[%d] = [ ", rep);

for (k=0; k<rows; k++) printf("%f   ",x[k]);

k=0;

printf("]\n");

printf("The length of this vector is %f\n", unit_norm(x, cols));

printf("Normalized new vector:\n");

printf("x[%d] = [ ", rep);

for (k=0; k<rows; k++) printf("%f   ",x[k]);

printf("]\n\n");

}

}


void matrix_mult(double K[4][4], double x[4], double y[4], int rows)

{

int j, i;

double dot_p;

for(i=0; i<rows; i++);

{

for(j=0, dot_p=0.; j<rows; j++)

{

dot_p += K[i][j] * x[j];

}

y[i] = dot_p;

}

return;

}


double unit_norm(double x[4], int cols)

{

double sum=0;

int i;

for (i=0; i<4; i++) sum += x[i] * x[i];

sum = sqrt(sum);

for(i=0; i<4; i++) x[i]=x[i]/sum;

return sum;

}

Results I should be getting:

Initial vector:

x[0] = [ 0.333333   0.666667  -0.333333   0.577350]


New vector:

x[1] = [-1.172650   2.744017  -3.315384   9.910319]

The length of this vector is: 10.867885

Normalized new vector:

x[1] = [-0.107900   0.252489  -0.305062   0.911890]


New vector:

x[2] = [-0.063865   2.716060  -4.176435  11.338931]

The length of this vector is: 12.385274

Normalized new vector:

x[2] = [-0.005157   0.219298  -0.337210   0.915517]

.... and so on until x[7] . Any ideas where I went wrong?

Thanks,
Rogan

[WingedPanther]

What results are you getting?

[rogan2915]

I'm getting the following results:

Initial vector:

x[0] = [ 0.333333   0.666667   -0.333333   0.577350   ]


New vector:

x[1] = [ -0.192450   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.653702

Normalized new vector:

x[1] = [ -0.052673   -0.136848   0.205271   0.967658   ]


New vector:

x[2] = [ 0.198632   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654033

Normalized new vector:

x[2] = [ 0.054360   -0.136835   0.205253   0.967570   ]


New vector:

x[3] = [ 0.198596   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654031

Normalized new vector:

x[3] = [ 0.054350   -0.136835   0.205253   0.967571   ]


New vector:

x[4] = [ 0.198597   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654031

Normalized new vector:

x[4] = [ 0.054350   -0.136835   0.205253   0.967571   ]


New vector:

x[5] = [ 0.198597   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654031

Normalized new vector:

x[5] = [ 0.054350   -0.136835   0.205253   0.967571   ]


New vector:

x[6] = [ 0.198597   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654031

Normalized new vector:

x[6] = [ 0.054350   -0.136835   0.205253   0.967571   ]


New vector:

x[7] = [ 0.198597   -0.500000   0.750000   3.535534   ]

The length of this vector is 3.654031

Normalized new vector:

x[7] = [ 0.054350   -0.136835   0.205253   0.967571   ]

[WingedPanther]

Well, for debugging purposes, I would start by adding some additional output to determine if the problem is with your addition or your multiplication functions. At a guess, you're finding x*K_transpose instead of x*K.