how to uses str2sym

clear all;clc

disp('------');

disp('The Nonlinear systems should be written in thefollowing form');

disp('Sliding Mode Controller for a class of Nonlinear systems');

disp(' State space equations x=f(x)+gu ');

disp('-----------');

n=input('Number of states:=');

nin=input('Number of inputs:=');

x=sym(zeros(1,n));

u=sym(zeros(1,nin));

par=input('Parameters ','s');

eval(sprintf('syms %s',par));

parameters=sprintf('%s',par);

for j=1:n

eval(sprintf('syms x%d',j))

x(:,j)=sprintf('x%d',j);

end

for k=1:nin

eval(sprintf('syms u%d',k));

u(:,k)=sprintf('u%d',k);

end

syms u

f=input('The vector f(x):=','s');

g=input('The vector g(x):=','s');

Hc=input('The output variables:=','s');

[Lhf,Lhg,dh,L,u,r]=NonContSidFed(f,g,Hc,x,u);

[Surf,dSurf,dd,K,Uc]=SlidingModeTerms(Hc,L,r,Lhg);

Answer 1

[Pranav Verma]

Hi Rim,

The str2sym function takes in a symbolic expression in a string form as input & evaluates it. Please refer to the below example illustrating the same:

>> st = '2+2';
>> str2sym(st)
 
ans =
 
4

Thanks

Answer 2

[Shubham Kumar Thakur]

syms t k;
ft1=input('Enter function of t (First part): ');
ft2=input('Enter function of t (Second part): ');
ft1= str2sym (ft1)
ft2= str2symm(ft2)
N=input('Enter No. of harmonics to be calculated: ');
t1=inpit('Enter first limit: ');
t2=inpit('Enter second limit: ');
t3=inpit('Enter third limit: ');
T=t3-t1; %Time Peiod
w0=(2*pi)/T; %Frequency
n=-N;1;N; %number of Harmonics (both sides)
Fn=(1/T)*(int((ft1*exp(-1j*n*w0*t)),t1,t2)+int((ft2*exp(-1j*n*w0*t)),t2,t3));
expar=exp(1j*w0*n*t);
tx=t1:0.001:t3; %Time vector for plotting
t=tx(:,1:end-1); nop=length(t); %no. of point in t
%plotting Input function

nop1=find(tx==t2)-find(tx==t1); nop2=find(tx==t3)-find(tx==t2);
t=tx(1:nop1); ftt1=eval(ft1).*ones(1,nop1);
t=tx(nop2+1:nop); ftt2=eval(ft2).*ones(1,nop2);
ft0=[ftt1 ftt2];
t=tx{:,1:end-1};