Surf function problem

2011 1 26
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I have a problem drawing a surface for a regression.
I have 3 vectors Y, X1, X2 and I have estimated the multiple linear regression: Y = c + a*X1 + b*X2 + u
I would like to draw the graph of this regression: Y = c + a*X1 + b*X2 + u using a MATLAB plot-graph.
I have tried the 'surf' function but I get this error 'Matrix dimensions must agree'.
I have done these things so far.
  1. Estimate the coefficients (c,a,b).
  2. Make a new serie [f=Y(estimated)], using the estimated coefficients (c,a,b). New serie: f = c + a*X1 + b*X2
  3. Use the 'surf' function. surf(X1,X2,f)
Can someone help me? I can’t understand what I am doing wrong.
PS: I use MATLAB 6.5*

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Sean de Wolski
Sean de Wolski 2011-1-26

1 个投票

You'll have to use
meshgrid
to generate your index matrices.
[X1 X2] = meshgrid(1:50);
c = pi;
a = 2;
b = -3;
f = c+a*X1+b*X2;
surf(X1,X2,f)
-Sean

更多回答（6 个）

Sean de Wolski
Sean de Wolski 2011-1-26

1 个投票

I.e. the known Y-values that you used for your regression? How about:
scatter3
or
plot3
to overlay them on your surface?
strat
strat 2011-1-26

0 个投票

Ohh...I forgot to use the meshgrid... Since X1,X2 have already their values, i didn't know that it needs the meshgrid. Thanks, i will keep in mind. ;) P.S Is there a way to add also the Y vector values at the 3-D graph? :)
strat
strat 2011-1-26

0 个投票

I have done the surface. Thanks again! :) Yep, Y are the known values. So now, how do i use the plot3, scatter3 to add the Y values?
strat
strat 2011-1-26

0 个投票

I think i am doing something wrong...:/ I wrote the code: figure; surf(X1,X2,f) hold on At scatter what i write? :? scatter3(X1,X2,f) ??

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Sean de Wolski
Sean de Wolski 2011-1-26
So you overwrote the original X1,X2 with the meshgrid X1,X2?
The call to scatter3 should be with the _original_ X1,X2 used for your regression and Y
scatter3(X1orig,X2orig,Y)

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strat
strat 2011-1-26

0 个投票

Nope, i used new series. Nevermind, It seems it had a glitch... Graph and Scatter is fine now.
Thanks a lot man! :thumbsup:

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