求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
hx=pi/nx;
x=linspace(0,pi,nx+1);
) x; i2 N+ x# f/ X# z+ Sy=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
" s+ c( S- I) [' S8 @3 \for i=1:nx+1
& N1 f) }" `8 v5 \& E# S$ {    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)
3 F! |  D2 c+ B    end;
3 }, ?. y* U. T6 Vend;
[xx,yy]=meshgrid(x,y);
. p" ?1 c6 W1 L/ m) r  \: tsurf(xx,yy,f_xx);
: t/ d( n5 q7 k0 X1 ~title('partial derivative w.r.t.xx')
0 v1 j' G, l5 Q. E/ [! a，
" T: e; D  k# V2 }7 O6 J
另开一个f9文件，
function l=f9(x,y)
9 u9 Y) v# G) ml=exp(sin(x-y));
' x7 Q* Q! n6 c' \% B
6 c- `! q) B1 V* I' t1 o, s: i' C
然后出来说错误了，
??? Input argument "x" is undefined.

) B/ t9 t9 [- v; e9 FError in ==> f9 at 2
1 T' ], E1 J  |/ Tl=exp(sin(x-y));
Error in ==> partial_derivxx at 11
$ o9 l" @; ~; k' ?8 d% ^        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

( [! D' ]+ e  L# z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~~~~~~~~~~~~~~~`