StartPoint function for General model Fourier1

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dai zhengguo 2017-6-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/343885-startpoint-function-for-general-model-fourier1

Here is the model(a0,a1,b1,w,x) = a0 + a1*cos(x*w) + b1*sin(x*w). I try to use curve fitting function. I want to find out the function [start, anError, aWarning] = iCheckStartPoint( start, model, probparams, xdata, ydata ), which is built in the funtion fit.m.(Matlab 2015a) How to compute the startpoint for the model(fourier1)? What's the meaning for the following code?

function [start, anError, aWarning] = iCheckStartPoint( start, model, probparams, xdata, ydata ) % iCheckStartPoint Ensure that the start point is valid. Throw errors or % warnings if it is not valid. anError = ''; aWarning = ''; numcoeff = numcoeffs( model );

% If the start point is empty, then use the model to estimate a start point if isempty( start ) startPointFcn = startpt( model );

    % If there is no function to estimate the start point, then we need to use a
    % random start point.
    if isempty( startPointFcn )
        aWarning = message( 'curvefit:fit:noStartPoint' );
        start = rand( numcoeff, 1 );
    else
        % Get constants for library functions
        someConstants = constants( model );
        try
            start = startPointFcn( probparams{:}, xdata, ydata, someConstants{:} );
        catch es
            anError = es;
            return
        end
    end
end

% Start points must be finite and real. if ~all(isfinite(start)) ~isreal(start) aWarning = message( 'curvefit:fit:invalidStartPoint' ); start = rand(size(start)); end

% There has to be exactly one start point per coefficient if numel( start ) < numcoeff anError = message( 'curvefit:fit:tooFewStartPoints', int2str( numcoeff ) ); return end if numel( start ) > numcoeff anError = message( 'curvefit:fit:tooManyStartPoints', int2str( numcoeff ) ); return end end