contour plot usage of argument v

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Yi Yang
Yi Yang 2016-8-10
评论： KSSV 2016-8-11
I am new to Matlab and I am learning the plot function 'contour'. One usage of it showed on the documentation is contour(X,Y,Z,v), the explanation of the argument v is not very clear in the documentation, could somebody give a thoughtful explanation and example on the usage of contour(X,Y,Z,v)?

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回答（2 个）

KSSV
KSSV 2016-8-10
v is used to specify the contour levels...Check the following code....it might clear you the concept..
clc ; clear all ;
x = -3:0.125:3;
y = -3:0.125:3;
[X,Y] = meshgrid(x,y);
Z = peaks(X,Y);
for i = 1:10
v = 1:i ;
contour(X,Y,Z,v) ;
fprintf('v is from %d to %d',1,i) ;
drawnow
pause(0.1)
end
  2 个评论
Yi Yang
Yi Yang 2016-8-10
Could you please be more specific on the 'level'? What if the elements in v are decimals? How are the levels calculated for a contour?
KSSV
KSSV 2016-8-11
It does interpolation and gets levels which does not exist....

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Star Strider
Star Strider 2016-8-10
The ‘v’ argument is a vector of values at which the contour lines are drawn, rather than having contour choose them.
Using an example from the documentation:
x = -3:0.125:3;
y = -3:0.125:3;
[X,Y] = meshgrid(x,y);
Z = peaks(X,Y);
v = [-3, -1, -0.5, 0.5, 5, 7];
figure
contour(X,Y,Z,v, 'ShowText','on')
This is especially useful for getting the zeros of a bivariate function:
x = -3:0.125:3;
y = -3:0.125:3;
[X,Y] = meshgrid(x,y);
Z = peaks(X,Y);
v = [0, 0];
figure
contour(X,Y,Z,v)

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