Z must be a matrix, not a scalar or vector

Question

Mike 2014-3-26

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/123233-z-must-be-a-matrix-not-a-scalar-or-vector

评论： Mike 2014-3-26

Hello,

I have run into this problem concerning a code i am writing to find a solution via the Monte Carlo method. Trying to plot my results on a meshgrid or surface, but i keep running into the Z must be a matrix issue. Can anyone spot my problem and give some advice on how to fix it?

Thanks

clear;
clc;
%--Number of simulations--%
n = 100; 
sol = linspace(0,1,n);
y = zeros(1,n);
x = zeros(1,n);
%--Plot of the circle--%
figure(1)
clf;
syms p
bc = sin (p);
bc2 = cos (p);
Range = [0 2*pi];
subplot(211);
h = ezplot(bc,bc2,[Range]);
hold on
[X,Y] = meshgrid(-1:0.1:1);
% 
Nsamples    = 5;
distance    = zeros(n,Nsamples);
circle      = zeros(n,Nsamples);
delta = 0.1;
% for loop2 = 1:Nsamples
    for t=1:n
          %--Monte Carlo Random Walk--%
          monte = randi(4,1);
          if monte == 1
              y = y + delta;
          elseif monte == 2
              y = y - delta;
          elseif monte == 3
              x = x + delta;
          elseif monte ==4
              x = x - delta;
          end
          %--Applying BC if sin is btween pi and 2pi--%
          %--Applying it by not allowing y >= 0--%
          if y < 0
              y = 0;
          end
          %--Solving for radius to see if BC's are hit--%
          radius = sqrt(x.^2 + y.^2);
          %--Calculating Theta for the BC--%
          theta = atan(y./x);
          %--Calcuating the solution with BC's--%
          if radius >= 1
              sol = sin(theta);
          elseif radius <= 0
              sol = 0;
          end
          %--Plotted walk on a circle plot--%
          subplot(211);
          plot(x,y,'.b');
          radius;
          sol;
          theta;
          %--Plotting Surface of Solution--%
          figure(2)
          mesh(X,Y,sol)
      end

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Answer 1

Mike Hosea 2014-3-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/123233-z-must-be-a-matrix-not-a-scalar-or-vector#answer_130607

It's telling you that the variable "sol" is a vector, whereas X and Y are matrices. If you want to plot a set of points on a surface, for every (X(i,j),Y(i,j)) pair the "mesh" function needs a Z(i,j), but that isn't provided by the sol vector. In fact, I don't see any connection at all between sol and the X and Y arrays.

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Mike 2014-3-26

Yeah, that makes sense. What i'm trying to do it plot the sol on a surface of an x and y range. That's what i thought i was doing, what would i need to change in order to do that?

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