Help with Basic 2D Contour Plot
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I am trying to get this contour plot to work. This is a simple example so I can figure out how to do it before applying it to trickier equations.
I have this function saved in a separate .m file:
function a = triarea(x,y)
a = x.^3-2.*x-5+y.^2;
end
The main script calls this function:
for s=[0:1:3],
for t=[0:1:3],
q=triarea(s,t)
end
end
This displays the range of values for q (one after the other, ideally I'd like them as one matrix upon completion but don't know how to do that).
What I want to do is a contour plot where the x-axis is the s variable and the y-axis is the t variable and q is represented as the contour i.e. varying in colour depending on it's value at each s,t point.
How do I do this?
It says that the contour variable Z must be at least a 2x2 matrix but I have only one value at each s,t point.
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Respuesta aceptada
Friedrich
el 10 de Mayo de 2013
Editada: Friedrich
el 10 de Mayo de 2013
Hi,
don't use a loop. Use meshgrid:
s=[0:1:3]
t=[0:1:3]
[X,Y] = meshgrid(s,t)
Z =triarea(X,Y);
contour(X,Y,Z)
This works as long the function triarea accepts matrices as input like it does in your example. Also you don't need to care about s and t (they dont need the same length and the values also doesn't matter).
s=-pi:0.1:pi;
t = 10:0.1:20;
[X,Y] = meshgrid(s,t)
Z =triarea(X,Y);
contour(X,Y,Z)
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Más respuestas (4)
John Doe
el 10 de Mayo de 2013
Editada: John Doe
el 10 de Mayo de 2013
Will this work for you?
q = zeros(4);
for s=[0:1:3],
for t=[0:1:3],
q(t+1,s+1)=triarea(s,t)
end
end
Note that this will only work if t and s contain only integers. If they do not:
s = [0:0.1:3];
t = [0:0.1:3];
q = zeros(length(s));
for i = 1:length(s)
for j = 1:length(t)
q(i,j) = triarea(s(i),t(j));
end
end
- Rob
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John Doe
el 10 de Mayo de 2013
Editada: John Doe
el 10 de Mayo de 2013
Follow the instructions from Friedrich, but flip the matrix around before you plot it.
Now, Z(1,1) is in the origin, Z(1,2) is in (0,1), Z(3,3) is in (2,2) etc. As you go downwards in Z, you move upwards on the Y-axis (in the plot).
ZZ = flipud(Z);
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