I have same values for all the 3 matrices

All the 3 matrices should show a diffent values but i get to see all are the same with a warning stating " The variable XXXX appeaqrs to change the sign on every loop iteration"

Here is the code:

for m=1:length(y)
    for n=1:length(x)
        r1source(m,n)=sqrt((x(n)-x1)^2+(y(m)-y1)^2);
        r2source(m,n)=sqrt((x(n)-x2)^2+(y(m)-y2)^2);
        r3source(m,n)=sqrt((x(n)-x3)^2+(y(m)-y3)^2);
    end
end

[Rik]

Without input data I don't see why the resulting matrices would be te same, nor where the warning would be coming from.

This can probably be done without a loop anyway, and if is can't you should replace length with numel, since that is probably what you mean.

Answer 1

[KSSV]

You need to initialize the variables which store data inside the for loop.

% Initilization 
r1source = zeros(length(y),length(x)) ; 
r2source = zeros(length(y),length(x)) ; 
r3source = zeros(length(y),length(x)) ; 
% loop 
for m=1:length(y)
    for n=1:length(x)
        r1source(m,n)=sqrt((x(n)-x1)^2+(y(m)-y1)^2);
        r2source(m,n)=sqrt((x(n)-x2)^2+(y(m)-y2)^2);
        r3source(m,n)=sqrt((x(n)-x3)^2+(y(m)-y3)^2);
    end
end

[Balaji Ramdas]

I am sorry that i was wrong in narrating the issue

code :

for m=1:length(y)
    for n=1:length(x)
        r1source(m,n)=sqrt((x(n)-x1)^2+(y(m)-y1)^2);
        r2source(m,n)=sqrt((x(n)-x2)^2+(y(m)-y2)^2);
        r3source(m,n)=sqrt((x(n)-x3)^2+(y(m)-y3)^2);
    end
end

for m1=1:length(y)
    for n1=1:length(x)
        r1measurement(m1,n1)=sqrt((x(n1)-x1)^2+(y(m1)-y1)^2);
        r2measurement(m1,n1)=sqrt((x(n1)-x2)^2+(y(m1)-y2)^2);
        r3measurement(m1,n1)=sqrt((x(n1)-x3)^2+(y(m1)-y3)^2);
    end
end


for m2=1:length(y)
    for n2=1:length(x)
        r1construction(m2,n2)=sqrt((x(n2)-x1)^2+(y(m2)-y1)^2);
        r2construction(m2,n2)=sqrt((x(n2)-x2)^2+(y(m2)-y2)^2);
        r3construction(m2,n2)=sqrt((x(n2)-x3)^2+(y(m2)-y3)^2);
    end
end

-------------------------------------------------------------------------------------------------------------------------------------------

What i see is r1 source, r1 measurement and r1construction has the same values,,,, similarly r2 and r3 ,,,, i suppose it has to be different

[KSSV]

They will be different if (x1,x32,x3) and (y1, y2, y3) are different. Check those values.

[Balaji Ramdas]

They are different

x1=0.4;

y1=0.2;

%source 2

x2=0.8;

y2=0.55;

%source 3

x3=0.5;

y3=0.65;

Thank you, i can see the warning sign after initialize step has vanished,

But i still see the matrices are the same for r1 soure, r1 construction, and r3construction ,,,,, and same for r2 and r3

[Rik]

Please attach your data or generate random example data. That way we can run it to reproduce your issue.

[Balaji Ramdas]

here is the entire script

[KSSV]

They are not same, they are different.

isequal(r1source,r2source)
isequal(r2source,r3source)
[min(r1source(:)) min(r2source(:)) min(r3source(:))]
[max(r1source(:)) max(r2source(:)) max(r3source(:))]

[Balaji Ramdas]

i mean the r1 source, r1 measurement, and r1 construction are the same

[KSSV]

Offcourse they will be equal as you have used the same formula to calclate both.

[Balaji Ramdas]

Got it,,, Thank you so much,,,,, One last question,, how to generate images to indicate pressure ?

[KSSV]

Read about pcolor.

figure(1)
pcolor(r1source)
shading interp
colorbar
figure(2)
surf(r1source)
shading interp
colorbar

[Balaji Ramdas]

Thank you so much

[KSSV]

Thanks is accepting/ voting the answer. :)

[Balaji Ramdas]

Just another question, how do i create the meausrement plane into imaginary ? as source plane the z axis value is zero but for the measurement plane it has to be an imaginary plane with z axis value of 0.2 from the real plane

%%source's positions
% source 1
x1=0.4;
y1=0.2;
z1=0;
%source 2
x2=0.8;
y2=0.55;
z2=0.2;
%source 3
x3=0.5;
y3=0.65;
z3=0.5;

f=1000; %Hz frequency
A1=1; %amplitude
w=2*pi*f; % angular speed
c=343; %m/s speed of sound in air
lambda=c/f; %m wave length
k0=w/c; %wave number
s=20; %matrix size
j=0.00001; % imaginary part

pref=2*10^-5; %Pa
p0=1.275; %kg/m3 air density


%aperture or Matrix size
x=linspace(1,0,s);
y=linspace(1,0,s);
z=linspace(1,0,s);

%Source plane

% Initilization 
r1source = zeros(length(y),length(x),length(z)) ; 
r2source = zeros(length(y),length(x),length(z)) ; 
r3source = zeros(length(y),length(x),length(z)) ; 

for m=1:length(y)
    for n=1:length(x)
        for o=1:length(z) 
            r1source(m,n,o)=sqrt((x(n)-x1)^2+(y(m)-y1)^2+(z(o)-z1)^2);
            r2source(m,n,o)=sqrt((x(n)-x2)^2+(y(m)-y2)^2+(z(o)-z2)^2);
            r3source(m,n,o)=sqrt((x(n)-x3)^2+(y(m)-y3)^2+(z(o)-z3)^2);
        end
    end
end

%Measurement plane

% Initilization 
r1measurement = zeros(length(y),length(x),length(z)) ; 
r2measurement = zeros(length(y),length(x),length(z)) ; 
r3measurement = zeros(length(y),length(x),length(z)) ; 

for m1=1:length(y)
    for n1=1:length(x)
        for o1=1:length(z)
            r1measurement(m1,n1,o1)=sqrt((x(n1)-x1)^2+(y(m1)-y1)^2+(z(o1)-z1)^2);
            r2measurement(m1,n1,o1)=sqrt((x(n1)-x2)^2+(y(m1)-y2)^2+(z(o1)-z2)^2);
            r3measurement(m1,n1,o1)=sqrt((x(n1)-x3)^2+(y(m1)-y3)^2+(z(o1)-z3)^2);
        end
    end
end