求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
. Y5 {! F4 G1 Cnx=50;
ny=30;
hx=pi/nx;
3 l* a' l- w: `  L% ]( b+ c- px=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
: ~/ e% q2 p* y$ |: W& ^7 c, Sx_minus_h=x-hx.*ones(1,nx+1);
for 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)
* p; w. w- ]* F! ^# l) y7 j3 j    end;
end;
  H7 }. w; D' A[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
' r/ B% |/ s* t- g$ ^& s7 Jtitle('partial derivative w.r.t.xx')
9 [1 B0 e. ~& H' G+ I7 D，
; e' E4 w/ E5 O
另开一个f9文件，
$ ?  g4 c' `! J1 `2 ]7 W% Ffunction l=f9(x,y)
l=exp(sin(x-y));
1 H% {, t! q  i4 N7 |# [
% ^5 a# E6 ?6 |0 r( b" R
然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
0 p$ l+ f6 _" J$ sl=exp(sin(x-y));
- y  i' y9 A  @& O/ u1 k. VError 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);
% j% j7 M4 D( |1 O) `; I3 f
- t9 Y8 k9 N; D; R. Y# z; I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~~~~~~~~~~~~~~~`