求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
' ]% }8 P! M& z8 M. g, L6 ~, l5 enx=50;
, I# z$ \3 m' o" p2 Sny=30;
* T/ C7 B2 t3 m+ whx=pi/nx;
- c, M# }# v2 h8 @/ U3 n! Gx=linspace(0,pi,nx+1);
, l9 N! r1 e! h7 e/ |y=linspace(0,pi,ny+1);
: `! v6 I9 ?' h' y6 Z5 P7 ~" F) L4 ix_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
1 N4 [4 b6 k: Q) Nfor i=1:nx+1
    for j=1:ny+1
1 k  Q2 i, H* z, w" v        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)
( r# j* m7 C$ N1 U    end;
end;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
$ n, q( R; i9 _title('partial derivative w.r.t.xx')
+ U9 I. U# v" J* u3 H+ b，
" j1 ~/ _* U* y5 z+ f% O; U  I. U
另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
4 T: T% E8 M: c" B: u7 `; I1 e

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

Error in ==> f9 at 2
l=exp(sin(x-y));
8 J1 O" G' u& @8 w- ?+ h: M- M, tError in ==> partial_derivxx at 11
- I4 e0 Q% s) b, n! T+ W; B/ h! _, ^        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
  K* a  h( v9 y7 k" V
0 R  R% Y) n# i4 C  M! L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~~~~~~~~~~~~~~~`