求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
! G5 C. v3 _- S- z1 lnx=50;
ny=30;
hx=pi/nx;
x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
# U& `- _2 |& m8 K8 B+ d9 Ix_plus_h=x+hx.*ones(1,nx+1);
x_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)
    end;
+ {- T1 c" ]5 v" o- Qend;
, e+ |$ ]3 ~2 W/ R[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，
) ~6 |9 ?0 Z3 A( N' E  t* K# N+ P& l
1 w: n1 [9 Y- t0 [8 A另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
+ C& s$ o5 B" p( M
* P( P. g" M5 h/ [8 |9 y
6 }; P/ ]* E4 N: N- m4 J9 r. `然后出来说错误了，
??? Input argument "x" is undefined.
/ {% b' v! ^6 ]. T+ k/ U
( U4 w/ S. C& n9 V, I7 N6 \Error in ==> f9 at 2
1 ]( U% x2 y. C3 Nl=exp(sin(x-y));
/ K- p* S, J: j& j5 O/ bError in ==> partial_derivxx at 11
, V$ z" I' G8 b1 y9 Z2 e: O' h5 i        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
8 K2 A* Q. O6 }" k
$ p6 a( I1 Y" @2 ~各位要怎么改才对呢

douglas8j

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

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

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

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))