MATLAB: Surf Plot using loops- Z must be a matrix, not a scalar or vector.

for loopsurf

Hello everyone,
I'm trying to plot a surface with the following code, but I keep getting this error. I don't know how to solve this, could someone help me?
Thanks in advance.
clear all;
% Welding parameters
%----------------------------
U = 28; %Voltage (V)
I = 260; %Current (A)
n = 0.9; %Efficiency 
Q = U*I*n; 
% Goldak Double-ellipsoid
%------------------------
a = 5; 
b = 6; 
C1 = 5; 
C2 = 20;
FF = 0.6;
FR = 1.4;
x = [-10:.2:10];
y= 0;
for z = -15:.05:15
    if z < 0
        C = C1;
        F = FF;
    else
        C = C2;
        F = FR;
    end
end
[xx,zz] = meshgrid(x,z);
A = ((6*sqrt(3)*F*Q)/(a*b*C*pi*sqrt(pi)));
B = exp(-3*(xx.^2/a.^2)).*exp(-3*(zz.^2/C.^2));
q = A*B;
surf (xx,zz,q)
Error using surf (line 57)
Z must be a matrix, not a scalar or vector.
Error in Goldak2 (line 34)
surf (xx,zz,q)

Best Answer

Hi Fabricio, the z vector does not survive (except for its last value) after the for loop. z is a scalar at that point. So you need to do something like
 z = -15:.05:15;
 for z1 = z
      if z1 < 0
          C = C1;
          F = FF;
      else
          C = C2;
          F = FR;
      end
  end
  [xx,zz] = meshgrid(x,z);
If you change the z spacing to something like .2 instead of .05, the plot is easier to see.
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