求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
. k  R6 R6 ~7 a6 f) Snx=50;
ny=30;
# W  ~- R7 c+ d9 N% Y; m" n: }+ Phx=pi/nx;
9 y7 w% d3 i( G+ }, c$ V7 Zx=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
7 P8 h% l# {4 |7 o8 T; I/ ~for i=1:nx+1
. f, z8 r# ^% I3 a7 b) l% W  G6 N- M    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)
5 }& R! w9 H" T3 w" E    end;
) L: `9 Z8 j3 ~% E& xend;
[xx,yy]=meshgrid(x,y);
7 C7 _( }% H" P& R' Hsurf(xx,yy,f_xx);
* `4 {! R6 g0 p  X- R1 \title('partial derivative w.r.t.xx')
，
+ \: ?0 x) K9 c9 |4 s
+ t  z  O0 k" b( t+ Z8 N另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));


然后出来说错误了，
: w5 Q* ]4 L  R7 J6 k* }??? Input argument "x" is undefined.

Error in ==> f9 at 2
5 k: M" N+ h' s$ k- v' h7 @7 nl=exp(sin(x-y));
; v4 g" U4 M  n  w  eError in ==> partial_derivxx at 11
        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

6 k8 ^) Z9 u& [( _) N; O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~~~~~~~~~~~~~~~`