求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
  x5 _* X  U% p$ [& }1 Lny=30;
* L$ W) j; @+ d& a: l' Uhx=pi/nx;
x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
0 U( y1 n7 y; F0 Ox_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
; [& Q3 e9 j5 G5 _6 u    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)
# T% _5 Z1 R7 m3 y    end;
end;
2 k% F0 q0 Z# ^& J! Z9 ?[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
. N0 e% |$ a. e

然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
* c4 O# Z5 b3 p/ z% ]l=exp(sin(x-y));
Error in ==> partial_derivxx at 11
+ g+ N3 ?7 T, w  B" q1 J, o* C        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
; m, V* c( u; r3 Q$ C
% E* F* R/ E  Z- T' P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~~~~~~~~~~~~~~~`