# Matrix manipulation and interpolation

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MSP on 19 Nov 2017
Commented: Jan on 20 Nov 2017
Hello here is my problem,Pls see the image for a simple understanding And thanks in advance
I have a matrix M (for easy visualization purpose a 3*3). I need to use this values to get a bigger matrix whose size is not neccessarily multiples of 3 (like 6*6)>It might be any number for example 11*11>Pls refer to image 2(matrix). So I want the the values to be interpolated and extapolated at the grey cells whereas the pink are my data points M. I have done upto this, where my input values can start from only index (1,1) which I dont want
m=magic(3)
S=size(m)
[Xi,Yi] = meshgrid(1:1:S(2),1:1:S(1));
[Xo,Yo] = meshgrid(1:0.5:S(2)+1,1:0.5:S(1)+1);
out = interp2(Xi,Yi,m, Xo,Yo)

Jan on 20 Nov 2017
Edited: Jan on 20 Nov 2017
Maybe you want to shifft the output one element to the right and bottom:
[Xo,Yo] = meshgrid(0.5:0.5:S(2)+0.5, 0.5:0.5:S(1)+0.5);
##### 2 CommentsShowHide 1 older comment
Jan on 20 Nov 2017
There is no unique method for extrapolating the values. You have to define at first, which model you want to use. Perhaps you want to repeat the existing marginal numbers, or fit a spline or B-spline to the data. Maybe you want a linear extrapolation or there is a fixed value on the edge.

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