IDL编程学习资料

15195775117

拟合与插值的联系？
拟合与插值有什么区别，是很多年隐隐浮现在我脑海的疑问，现在看来，拟合的要求高，插值的要求低，因为拟合是要有公式的，插值则没有公式，拟合必须使用既有的数学公式，而且如何达到最精确，是个颇有难度的问题。根据已有的点进行插值则比较自由。

15195775117

非线性拟合之LMfit

似乎很有应用价值哟

                               
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The LMFIT function does a non-linear least squares fit to a function with an arbitrary number of parameters. LMFIT uses the Levenberg-Marquardt(列文伯格-马夸尔特) algorithm, which combines the steepest descent(最速下降法) and inverse-Hessian(海森) function fitting methods. The function may be any non-linear function.

Iterations are performed until three consecutive iterations fail to change the chi-square value by more than the specified tolerance amount, or until a maximum number of iterations have been performed. The LMFIT function returns a vector of values for the dependent variables, as fitted by the function fit.

The initial guess of the parameter values should be as close to the actual values as possible or the solution may not converge(还是要先验值啊). Test the value of the variable specified by the CONVERGENCE keyword to determine whether the algorithm converged, failed to converge, or encountered a singular matrix.

15195775117

多项式拟合poly_fit

The POLY_FIT function performs a least-square polynomial(多项式) fit with optional weighting(权重) and returns a vector of coefficients.

The POLY_FIT routine uses matrix inversion to determine the coefficients.A different version of this routine, SVDFIT, uses singular value decomposition (SVD). The SVD technique is more flexible and robust(鲁棒), but may be slower.

既然SVDfit更好，还要poly_fit作甚？

jinhai

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