求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
7 r* r! B9 |/ _, r8 F& E6 [  @nx=50;
' {/ y' `- E6 M( `ny=30;
# E* n0 A7 o, q$ b1 z5 J2 whx=pi/nx;
x=linspace(0,pi,nx+1);
2 R2 D3 t' g% t# t; W- p! `y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
$ L( r2 w; |2 U2 A& E( V  [+ ]x_minus_h=x-hx.*ones(1,nx+1);
; c7 X/ ?1 f% |3 ofor i=1:nx+1
8 g8 p, `7 s" H4 X% Y    for j=1:ny+1
        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);   %原式f(x+hx,y)-2f(x,y)+f(x-hx,y)./(hx^2)
    end;
end;
[xx,yy]=meshgrid(x,y);
$ r. \- L; @9 o4 q% q9 U5 Tsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
+ Y8 F9 @; G( ~! _，

! |; [  |& U2 l6 R$ ^3 W另开一个f9文件，
* O, ]1 J1 h) P4 Y; _function l=f9(x,y)
l=exp(sin(x-y));

  w3 M1 v& {& Y  L
然后出来说错误了，
$ L1 ^" x7 c  @??? Input argument "x" is undefined.

' @4 ]' R2 k5 ^) _: {. BError in ==> f9 at 2
l=exp(sin(x-y));
Error in ==> partial_derivxx at 11
7 {- |6 u! F7 o! i0 m: V        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

各位要怎么改才对呢

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))

douglas8j

abc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

henhaodeyipianwenzhang~~~~~~~~~~~~~~~`