MATLAB: Math Question_ Combination

mathematicsMATLABmatrix

Hi,

Let say i have 10 location. I wana test 3 location at a time.

i think there are 10C3=120 combination.(assuming order of the location is not important).

My question is how do i list all the combination in an array?

For example [1 2 3,1 2 4, 1 2 5 ,. . . . . till the 120th]

Best Answer

nchoosek(1:10,3)

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MATLAB: How to select value

clear
Z=[-4:1:2];
H=[0:1:4];
[xx,yy]=meshgrid(Z,H);
zz=0.4166+0.0456.*yy-0.2343.*xx;
zz(zz>1)=1
zz(zz<0)=0
figure
surf(xx,yy,zz)

MATLAB: Error in surfnorm function

The surfnorm function requires the Z input to be at least a 3x3 matrix because it uses a Taylor Series to predict the next surface point beyond the given inputs.

In this particular case, the surface mesh boundaries are predetermined, and the mesh is coarse. The combination of these two characteristics can create a very large 2nd derivative of the surface in the Taylor Series Prediction. In this case, the extended boundary was actually folded back inside the input surface.

I don't like altering built-in Matlab functions, but I fixed the problem by removing the 2nd derivative from the Taylor Series prediction...

Replace lines 81-87 of the surfnorm function with the following:

% % Expand x,y,z so interpolation is valid at the boundaries.

% xx = [3*xx(1,:)-3*xx(2,:)+xx(3,:);xx;3*xx(m,:)-3*xx(m-1,:)+xx(m-2,:)];

% xx = [3*xx(:,1)-3*xx(:,2)+xx(:,3),xx,3*xx(:,n)-3*xx(:,n-1)+xx(:,n-2)];

% yy = [3*yy(1,:)-3*yy(2,:)+yy(3,:);yy;3*yy(m,:)-3*yy(m-1,:)+yy(m-2,:)];

% yy = [3*yy(:,1)-3*yy(:,2)+yy(:,3),yy,3*yy(:,n)-3*yy(:,n-1)+yy(:,n-2)];

% zz = [3*zz(1,:)-3*zz(2,:)+zz(3,:);zz;3*zz(m,:)-3*zz(m-1,:)+zz(m-2,:)];

% zz = [3*zz(:,1)-3*zz(:,2)+zz(:,3),zz,3*zz(:,n)-3*zz(:,n-1)+zz(:,n-2)];

%% GJE Alteration

% Expand x,y,z so interpolation is valid at the boundaries.

xx = [xx(1,:)+ (xx(1,:)-xx(2,:)) ;xx; xx(m,:)+ (xx(m,:)-xx(m-1,:))];

xx = [xx(:,1)+ (xx(:,1)-xx(:,2)) ,xx, xx(:,n)+ (xx(:,n)-xx(:,n-1))];

yy = [yy(1,:)+ (yy(1,:)-yy(2,:)) ;yy; yy(m,:)+ (yy(m,:)-yy(m-1,:))];

yy = [yy(:,1)+ (yy(:,1)-yy(:,2)) ,yy, yy(:,n)+ (yy(:,n)-yy(:,n-1))];

zz = [zz(1,:)+ (zz(1,:)-zz(2,:)) ;zz; zz(m,:)+ (zz(m,:)-zz(m-1,:))];

zz = [zz(:,1)+ (zz(:,1)-zz(:,2)) ,zz, zz(:,n)+ (zz(:,n)-zz(:,n-1))];

Regards, Gabe

Best Answer

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MATLAB: How to select value

MATLAB: Error in surfnorm function

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