从 sfit 对象获取均值和标准差

Question

加载完成后，预拟合曲面（sfit）模型如下图所示。

问题：如何从 sfit 对象中获取 x/y 数据的精确 mean/std（而不是从输出中进行繁琐的复制）？

备注：

我可以通过调用其 coeffnames/coeffvalues API 来获取所有系数。但是，mean/std.
当前无法访问sfit模型拟合的原始数据。所以the method依赖原始数据是不适用的。

Answer 1

查看sfitclass的来源，原来均值和标准差存储在private属性中meanx，meany, stdx, stdy。这些都是 private 的事实使这项工作变得非常重要，但是 thanks to Yair Altman we know that 在 class 上调用 struct() 通常会揭示它的所有优点。

使用 sfit documentation、

中稍作修改的示例

x = 3 - 6 * rand( 49, 1 );
y = 3 - 6 * rand( 49, 1 );
z = peaks( x, y );
sf = fit( [x, y], z, 'poly32', 'normalize', 'on');

这是我们看到的：

>> sf

     Linear model Poly32:
     sf(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2 + p30*x^3 + 
                    p21*x^2*y + p12*x*y^2
       where x is normalized by mean -0.3736 and std 1.887
       and where y is normalized by mean -0.04893 and std 1.644
     Coefficients (with 95% confidence bounds):
       p00 =      0.4227  (-0.3731, 1.218)
       p10 =       1.764  (0.5627, 2.965)
       p01 =       1.313  (0.7715, 1.855)
       p20 =     -0.1054  (-0.6496, 0.4389)
       p11 =      0.4627  (0.03944, 0.8859)
       p02 =      0.1898  (-0.2443, 0.6239)
       p30 =     -0.6345  (-1.247, -0.02209)
       p21 =     -0.8263  (-1.32, -0.3327)
       p12 =     -0.4908  (-1.011, 0.02911)

>> sf_struct=struct(sf)
Warning: Calling STRUCT on an object prevents the object from hiding its implementation details and should thus be avoided. Use DISP or
DISPLAY to see the visible public details of an object. See 'help struct' for more information. 

    sf_struct = 

                 version: 2
            fCoeffValues: {[0.4227]  [1.7639]  [1.3130]  [-0.1054]  [0.4627]  [0.1898]  [-0.6345]  [-0.8263]  [-0.4908]}
             fProbValues: {1x0 cell}
                     sse: 59.5574
                     dfe: 40
                    rinv: [9x9 double]
            activebounds: [9x1 logical]
                   meanx: -0.3736
                   meany: -0.0489
                    stdx: 1.8875
                    stdy: 1.6441
                    xlim: [-2.8236 2.8090]
                    ylim: [-2.7585 2.6763]
                   fType: 'poly32'
               fTypename: 'Poly32'
               fCategory: 'library'
                    defn: 'p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2 + p30*x^3 + p21*x^2*y + p12*x*y^2'
                  fFeval: 1
                    expr: @polySurface
                   Adefn: {}
                   Aexpr: {}
                  linear: 1
                 derexpr: @polySurfaceDerivative
                 intexpr: []
                    args: [11x3 char]
                 isEmpty: 0
                 numArgs: 11
               numCoeffs: 9
             assignCoeff: [1x234 char]
              assignData: ' x = FITTYPE_INPUTS_{10}; y = FITTYPE_INPUTS_{11};'
              assignProb: ''
                   indep: [2x1 char]
                   depen: 'z'
                   coeff: [9x3 char]
                    prob: ''
              fConstants: {[3]  [2]}
        fNonlinearcoeffs: []
             fFitoptions: [1x1 curvefit.llsqoptions]
                fStartpt: []

>> [sf_struct.meanx, sf_struct.meany, sf_struct.stdx, sf_struct.stdy]

    ans =

       -0.3736   -0.0489    1.8875    1.6441

至少在 R2012b 中以上内容有效。

从 sfit 对象获取均值和标准差

Get mean and std from sfit object

matlab

data-fitting