contour plot usage of argument v

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)?

Answer 1

[KSSV]

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

[Yi Yang]

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]

It does interpolation and gets levels which does not exist....

Answer 2

[Star Strider]

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)