Creating a phase portrait of first order equations using meshgrid and quiver

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Blake 2015-9-29

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https://ww2.mathworks.cn/matlabcentral/answers/245663-creating-a-phase-portrait-of-first-order-equations-using-meshgrid-and-quiver

评论： Madhav Rajan 2015-10-1

I have the script set up the way I think it should be however the the equation dx/dt=Ax where x is an nx1 solution vector and A is a constant matrix. The x and y intervals are [-2.5:2.5]. Should n also be given in order for me to be able to finish writing this function. The function should take in a matrix A and return the phase portrait.

function [ ] = directionField( A )
 x=-2.5:2.5
 y=-2.5:2.5
[x,y]=meshgrid(x, y);
dy=A.*?
dx=ones(size(x));
veclength= sqrt(dx.^2+dy.^2);
v=dy./veclength;
u=dx;
scale=0.5
quiver(x,y,u, v,scale)
end

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Madhav Rajan 2015-10-1

I understand that you want to know whether you need the variable 'n' in order to write this function. Since you know the size of 'x', 'n' is not needed but as pointed out in the documentation , the following condition must be satisfied:

length(x) = n and length(y) = m, where [m,n] = size(u) = size(v)

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