function z=fun2( a, y)
z=a1* y(1,:).*(1 - y(2,:)./(0.9)+a2* y(2,:)+a3* y(3,:);

x1=[-1.42075 -1.20149 -0.92967 -0.61992 -0.13172 0.4723 0.80628 0.98561 1.43674  ];
x2=[0.43 0.69 0.81 1.03 1.12 1.21 1.28 1.35 1.42];
x3=[-0.58377  -0.21715  -0.43883  -0.46332  -0.31833  -0.44273  2.77192  0.25288  -0.24275  ];
y=[x1;x2;x3];a0=[1,1,1];
z=[0.21926  0.27182  0.30975  0.4882  0.60402  0.33398  0.17933  0.45113  -0.83412];
a=lsqcurvefit('fun2',a0, y,z)


出错 lsqcurvefit (line 202)
            initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});

原因:
    Failure in initial objective function evaluation. LSQCURVEFIT cannot continue
运行的过程中一直出现这样的问题，不知道怎么解决。
原方程 Y=a1*x*( 1-y/0.9)+a2*y+a3*z;