功能: 计算模型在指定处一阶导数的值

格式: PeakVibrationCalcFirstDiff(obj, x)

obj : {PeakVibrationCreate<矩阵运算/PeakVibrationCreate>}创建或者振动-多峰工具箱窗口优化得到的模型对象。
x   : 数值或矩阵变量,里面存储对应点自变量的值。

说明:
1、本函数主要计算模型一阶导数值

例子:
n = [ 1 1 2 1 1 0 ];
p =
[ 295845834.351268
 -168499.433596370
  0.08015859458975
 -462016.749564439
 -9768.24709729634
  263.611207456596
 -10.5633972790198
  0.86124003876391
  1.15360561518295
 -61.1969436802180
 -0.66865654417505
  0.32975728694554
  1.00526588654014
  2.36972517149763
  2.61681327858656
 -300418369509.681
  477.776139642666
  5.19585763105866
  23986519890.6085
  89.8494991514260
  16.4920376966502 ];
obj = {PeakVibrationCreate<矩阵运算/PeakVibrationCreate>}(n, p);//创建模型
t  = [1.5 2.3];//预测1.5与2.3处的一阶导数值
dy = PeakVibrationCalcFirstDiff(obj,t)//回车得到如下结果
dy =
[ 0.78298733659903   -0.90604969349806 ]