System identification for given data pairs

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Kushal Badgujar
Kushal Badgujar 2014-8-24
评论： Star Strider 2014-8-24
Hello
I have system with 3 input and one output. This is "time independent" system. How can we express this system with polynomial fit or other methods relating input and output ?
regards Kushal
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Kushal Badgujar
Kushal Badgujar 2014-8-24
编辑：Kushal Badgujar 2014-8-24
Furthermore is it possible to obtain inverse of this system i.e. given output y find input u1,u2, u3 ?

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Image Analyst
Image Analyst 2014-8-24
There may be many u1,u2,u3 that give rise to a certain output value, y, especially if they are integers. If your y is a 3D array of numbers for every u1,u2,u3 (for example it's the intensity value of a 3D CT or MRI medical image), you can find the logical indexes for places with that y value like:
locations = find(y == desired_y);
For the fitting question, John D'Errico has a polyfitn() that will fit a 3D polynomial to your data. http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A679

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