求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
6 b7 s5 d# r6 F5 V' |ny=30;
+ h& M$ e, D* s' k0 Z9 lhx=pi/nx;
- s9 \  v# u# v5 U) ex=linspace(0,pi,nx+1);
2 t+ x1 a( R1 V5 J' L! S1 M+ f) dy=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
7 B- F2 B2 h* l9 R2 lfor i=1:nx+1
    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)
6 S# S8 C9 r5 E! t7 h, _7 z( z    end;
& a9 n: W. L8 t- h$ m7 G. oend;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
9 m. z9 ]( S  i$ Y- ~( b: i6 _* Ntitle('partial derivative w.r.t.xx')
，

) d3 h7 ^# a1 u, a另开一个f9文件，
4 I  u$ l9 d2 e( C0 T' T+ mfunction l=f9(x,y)
: U' R* v6 b" v. e: |/ p* N7 zl=exp(sin(x-y));

3 o3 E) |* Y* a5 a+ _8 Y* _! ^
然后出来说错误了，
2 T8 h' d% _' _9 @% {5 ~??? Input argument "x" is undefined.
& D- l1 K. v: v: L& I) q8 E
  I3 m% w! C% M9 R3 R& FError in ==> f9 at 2
# f5 [( _* O# j* d( f# Zl=exp(sin(x-y));
. F' s5 }/ l; F" t! m' O4 J; ~" TError in ==> partial_derivxx at 11
        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
* K: x8 w+ ]& z' v0 G6 d  r
8 o9 N9 v. l+ b$ R: D& L$ O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~~~~~~~~~~~~~~~`