Help! Plotting.

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2 total messages Started by Dennis Woo Sun, 24 Jan 1993 23:34

#38

Author: Dennis Woo
Date: Sun, 24 Jan 1993 23:34

31 lines
1315 bytes

Hi Matlab expert,

I am trying to make a contour plot of a hyperparaboloid of a
two-variable function. The equation look like this:

 z = 2*w0^2 + 3*w1^2 - 12*w0 - 8*w1 + 2*w0*w1 + 36

The minimum of z(w0,w1) is z(2.8,0.4)=17.6.

I entered the following lines in matlab:
	
  [w0,w1]=meshdom(-5:.1:5,-5:.1:5);
  z = 2*(w0.^2) + 3*(w1.^2) - 12*w0 - 8*w1 
      + 2*(w0.*w1) + 36*ones(w0);
  contour(z)

Instead of contours (these contours are ellipses) centered at (2.8,0.4)
with a z-value of 17.6,  I got the contours centered at around
(85,60).

Could someone please let me know what I have done wrong.

Thanx a lot. 

New Matlab user,
*****************************************************************
*  Dennis Woo              Department of Mechanical Engineering *
*  E-mail: dwoo@unb.ca     University of New Brunswick          *
*  Tel: (506) 453-4513                                          *
*****************************************************************

Re: Help! Plotting.

#60

Author: Michael Maurer
Date: Mon, 25 Jan 1993 21:45

23 lines
1263 bytes

In <1993Jan24.233400.1494@jupiter.sun.csd.unb.ca> dwoo@jupiter.sun.csd.unb.ca (Dennis Woo) writes:

>I entered the following lines in matlab:
>	
>  [w0,w1]=meshdom(-5:.1:5,-5:.1:5);
>  z = 2*(w0.^2) + 3*(w1.^2) - 12*w0 - 8*w1 
>      + 2*(w0.*w1) + 36*ones(w0);
>  contour(z)

>Instead of contours (these contours are ellipses) centered at (2.8,0.4)
>with a z-value of 17.6,  I got the contours centered at around
>(85,60).

Your mistake is to omit the axes specifications to 'contour'.  Without
these, 'contour' will use the indices into the array 'z' as the x- and
y-axes.  Instead you should say

contour(z,-5:.1:5,-5:.1:5)

Good luck.
--
______________________________________________________________________
Michael Maurer          maurer@nova.stanford.edu        (415) 723-1024

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