錯(cuò)誤：??? Error using ==> sym.sym>assumptions at 2180Second argument f not recognized.Error in ==> sym.sym>tomupad at 2156assumptions(S,x.s,a);Error in ==> sym.sym>sym.sym at 114S.s = tomupad(x,a);Error in ==> vpa at 55ss = sym(s,'f');Error in ==> ex0804 at 18A_sym(1)=double(VPA(A0,Nn));代碼：% [ex8.4] 周期方波脈沖及單邊頻譜function [A_sym,B_sym]=CTFSdbfb(T,Nf,Nn)% 采用符號(hào)計(jì)算求[0,T]內(nèi)時(shí)間函數(shù)的三角級(jí)數(shù)展開系數(shù)。% 函數(shù)的輸入輸出都是數(shù)值量% Nf 諧波的階數(shù)% Nn 輸出數(shù)據(jù)的準(zhǔn)確位數(shù)% A_sym 第1元素是直流項(xiàng)，其后元素依次是1,2,3...次諧波cos項(xiàng)展開系數(shù)% B_sym 第2,3,4,...元素依次是1,2,3...次諧波sin項(xiàng)展開系數(shù)syms t n k y T=5;if nargin<4;Nf=input('plear Input 所需展開的最高諧波次數(shù):');endT=5;if nargin<5;Nn=32;endy=time_fun_s(t);A0=2*int(y,t,0,T)/T;As=int(2*y*cos(2*pi*n*t/T)/T,t,0,T);Bs=int(2*y*sin(2*pi*n*t/T)/T,t,0,T);A_sym(1)=double(VPA(A0,Nn));for k=1:NfA_sym(k+1)=double(vpa(subs(As,n,k),Nn));B_sym(k+1)=double(vpa(subs(Bs,n,k),Nn));endif nargout==0 S1=fliplr(A_sym) %對(duì)A_sym陣左右對(duì)稱交換  S1(1,k+1)=A_sym(1) %A_sym的1*k陣擴(kuò)展為1*(k+1)陣S2=fliplr(1/2*S1) %對(duì)擴(kuò)展后的S1陣左右對(duì)稱交換回原位置S3=fliplr(1/2*B_sym) %對(duì)B_sym陣左右對(duì)稱交換  S3(1,k+1)=0 %B_sym的1*k陣擴(kuò)展為1*(k+1)陣S4=fliplr(S3) %對(duì)擴(kuò)展后的S3陣左右對(duì)稱交換回原位置S5=S2-i*S4;  N=Nf*2*pi/T;k2=0:2*pi/T:N;subplot(3,3,3)x=squ_timefun(t,T) %調(diào)用連續(xù)時(shí)間函數(shù)-周期方波脈沖T=5;t=-2*T:0.01:2*T;plot(t,x)title('周期方波脈沖')axis([-10,10,-1,1.2])line([-10,10],[0,0])subplot(3,1,3)stem(k2,abs(S5)); %畫出周期方波脈沖的頻譜（脈寬a=T/2）title('周期方波脈沖的單邊頻譜')axis([0,60,0,0.6])end%-------------------------------------------function y=time_fun_s(t)% 該函數(shù)是CTFSdbfb.m的子函數(shù)。它由符號(hào)變量和表達(dá)式寫成。syms a a1T=5;a=T/2;y1=sym('Heaviside(t)')*2-sym('Heaviside(t-a1)');y=y1-sym('Heaviside(t+a1)');y=subs(y,a1,a);y=simple(y);%------------------------------function x=squ_timefun(t,T)% 該函數(shù)是CTFSdbfb.m的子函數(shù),它由方波脈沖函數(shù)寫成。% t 是時(shí)間數(shù)組% T 是周期 duty'占空比'：信號(hào)為正的區(qū)域在一個(gè)周期內(nèi)所占的百分T=5;t=-2*T:0.01:2*T;duty=50;x=square(t,duty);