求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
9 R& `7 C4 U( Dnx=50;
ny=30;
hx=pi/nx;
x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
1 `5 T/ @% j( T/ r/ rx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
% A/ D3 W- ]8 K8 _    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;
0 I7 Q8 N5 E  L* x, W% Q4 U[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
. P$ h1 B6 k& y7 t+ \: j
另开一个f9文件，
* R$ |5 @) c$ Q. T( i; Mfunction l=f9(x,y)
5 v5 F" r& x8 @7 S: C- L) Ul=exp(sin(x-y));
3 d& B* y) l1 H) a

7 V; U- p. w3 s3 `然后出来说错误了，
( F8 A; G( F) A, b+ w??? Input argument "x" is undefined.

3 `2 R  b/ g8 V1 AError in ==> f9 at 2
! Q& A8 A6 d% F( L+ ^! ]" S4 \l=exp(sin(x-y));
& T) c: n# m0 nError in ==> partial_derivxx at 11
- d# K# ^% V. p3 t' ~7 G        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
+ }# [4 h+ l/ Z8 G" N3 z
. F3 g" Z' e% W1 A* B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~~~~~~~~~~~~~~~`