Assign discrete values to meshgrid elements

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Ritwik Rakshit
Ritwik Rakshit le 12 Fév 2019
Commenté : Walter Roberson le 12 Fév 2019
I have a system of differential equations that takes in a pair of scalars (say C and D) and outputs a scalar E after evaluating the system numerically. I'm able to generate multiple E-values for an array of C- and D-values by using nested for loops. How can I plot the resulting values as a surface against a grid of the independent variables, rather than as a 3D scatter plot?
E is essentially a function of C and D, but cannot be expressed in closed form and must be evaluated numerically.
for i=1:n
C=0.1*i;
for j=1:n
D=0.01*j;
while ti<to
[t, y]=ode23(@myFunction, [ti to], [0; 0; 0]);
E(i,j)=y(end, 2);
end
end
end
% The following code will work, but the axes won't be oriented correctly
[C,D]=meshgrid(0:0.1:0.1*n,0:0.01:0.01*n);
surf(C,D,E);

Réponse acceptée

Walter Roberson
Walter Roberson le 12 Fév 2019
Switch to surf(C, D, E.') or else change meshgrid to ndgrid()
  2 commentaires
Ritwik Rakshit
Ritwik Rakshit le 12 Fév 2019
Transposing worked perfectly. Is there any documentation about the interaction of meshgrid and surf, or why transposition is necessary?
Walter Roberson
Walter Roberson le 12 Fév 2019
The syntax is surf(X, Y, Z) , and all three matrices must be the same size. But in MATLAB X is the rows and Y is the columns .
[C, D] = meshgrid( 1:M, 1:N)
gives C as being N x M but
for i : M
for j = 1 : N
E(i, j) = something
end
end
gives E as M x N.

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