??? Attempted to access V(4.15712e+008); index must be a positive integer or logical. Error in ==> modallllll at 50 an = (w * p0*c0^2)/V(2 * damping *wn*w +1*(w^2 -wn^2)) * p_xyz_t;

Hi, I am having a logical error with V and had a go at fixing it using the logical function and unfortunately had no luck.

This is my code

close all;

clear all;

ampl = 1;

l_x = 5; % meters

l_y = 6; % meters

l_z = 4;

step = 0.0125; % meters

n_x = 4; % modal index

n_y = 3; % modal index

x_vector = 0: step: l_x;

y_vector = 0: step: l_y;

length_y = length (y_vector);

length_x = length (x_vector);

p_xyz_t = zeros (length_x,length_y);

c = 341; %m/s

X= (n_x)/(l_x);

Y =(n_y)/(l_y);

f_acoust = (c/2)*sqrt(X^2+Y^2);

period = 1 / f_acoust;

nbr_of_frames = 90;

f_sampling = 20* f_acoust; % Hz

delta_t = 1 / f_sampling; % seconds

for idx_t = 1 : nbr_of_frames

for idx_x = 1: length_x

p_xyz_t (idx_x, :) = ampl * cos(2*pi*idx_t*delta_t/period)*...

cos(n_x*pi*(idx_x-1)*step/l_x) * cos((n_y*pi*y_vector/l_y));

end

end

%%%for single point monopole source at rq

w = 2 * pi * f_sampling;

p0 = 1.204;

c0 = 341;

V = 60;

damping = 0.2;

wn = f_acoust * 2 * pi;

p_xyz_t = logical(p_xyz_t);

V = logical(V);

an = (w * p0*c0^2)/V(2 * damping * wn * w +1*(w^2 -wn^2)) * p_xyz_t;

figure(1) contour( p_xyz_t); axis ([1, length_y, 1, length_x, -1.5*ampl, 1.5*ampl ]);

figure(2) surf( p_xyz_t); axis ([1, length_y, 1, length_x, -1.5*ampl, 1.5*ampl ]);

Answer 1

[Andreas Goser]

It is in this expression:

V(2 * damping * wn * w +1*(w^2 -wn^2))

V is a scalar (1x1 matrix) in your code and cannot be indexed.

You propbably want to do something completely different.

Answer 2

[Azzi Abdelmalek]

Use

V(int64(2 * damping * wn * w +1*(w^2 -wn^2)))

[Clarissa]

When I used that it came up with a new error

??? Index exceeds matrix dimensions.

Error in ==> modallllll at 50 an = (w * p0*c0^2)/V(int64(2 * damping wn * w +1(w^2 -wn^2))) * p_xyz_t;