Maximum X value for maximum calculation obsurd

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Gavin Seddon 2015-9-22

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编辑： Jan 2015-9-23

xHello using fminbnd to calculate a maximum, the resulting X value calculated is nought .9 whereas it should be about 3100. Can anyone suggest a reason for this? It appears that the curve in curve fitting tool is perfect however it doesn't appear to start at 0 where it should. Can anyone help please? Gavin.

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Answer 1

Walter Roberson 2015-9-22

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fminbnd is a local minimizer.

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John D'Errico 2015-9-22

编辑：John D'Errico 2015-9-22

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PLEASE use comments instead of adding new answers for every comment. I have moved Gavin's comment into a comment from an answer by him:

Will you tell me a global minimiser along with its handler please?
It seems odd that the fminbnd command accepts limits yet minimises below them.

Gavin Seddon 2015-9-23

编辑：Jan 2015-9-23

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Hello Walter, remember I am finding the maximum using -f. I fixed the problem using your comment. I redefined f as

f =  @(x)-(p1.*x.^8+p2.*x.^7+p3.*x.^6+p4.*x.^5+p5.*x.^4+p6.*x.^3+p7.*x.^2+p8.*x+p9)

and then created the new handler, minusF = @(x) -f(x) and finally used

x = fminbnd(minusF,0, 3200)

this works but it gives

x = 3.2000e+03

Which is the maximum defined boundary. the curve appears to have a derivative of 0. Therein would you suggest defining this point to be at a position in which the Y variable varies less? Gavin.

[EDITED, Jan, Code formatted]

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