How can I define a piecewise function by using Matlab

How can I define piecewise function by using matlab and use it than to calculate Galerkin method my attempt was as follow:

clc;
clear all,
close all,
g=1;
syms x;
%  this is piecewise function 
%     y=[y1 y2 y3];
%     If (x>=-1 && x<=-0.5) then
    y1=(2*x)+2;  
%    If (x>=-0.5 && x<=0) then 
    y2= -2*x;
%     If (x>=0 && x<=1) then
    y3=0;
% % % % % 
%     z=[z1 z2 z3 z4];
%   If (x>=-1 && x<=-0.5) then  
    z1=0;
%     If (x>=-0.5 && x<=0) then
    z2= 1+2*x;
%     If (x>=0 && x<=0.5) then
    z3=1-2*x;
%     If (x>=0.5 && x<=1) then
    z4=0;
% % % % % 
%     q=[q1 q2 q3];
%   If (x>=-1 && x<=0) then 
    q1=0;
%     If (x>=0 && x<=0.5) then
    q2= 2*x;
%     If (x>=0.5 && x<=1) then
    q3=2-2*x;
% % % % % 

C(1,1)= int(((diff(y1))^2),-1,-0.5)+ int(((diff(y2))^2),-0.5,0);
C(2,2)= int(((diff(z2))^2),-0.5,0)+ int(((diff(z3))^2),0,0.5);
C(3,3)= int(((diff(q2))^2),0,0.5)+ int(((diff(q3))^2),0.5,1);
C(1,2)= int(((diff(y2))*(diff(z2))),-0.5,0);
% it is symmtric
% C(2,1)= int(((diff(z2))*(diff(y2))),-0.5,0);
C(2,1)=C(1,2);
C(1,3)= 0;
C(3,1)= 0;
C(2,3)= int(((diff(z3))*(diff(q2))),0,0.5);
% it is symmtric
% C(3,2)= int(((diff(q2))*(diff(z3))),0,0.5);
C(3,2)=C(2,3);
 f(1,1)=(int(y1,-1,-0.5))+(int(y2,-0.5,0));
 f(2,1)=(int(z2,-0.5,0))+(int(z3,0,0.5));
 f(3,1)=(int(q2,0,0.5))+(int(q3,0.5,1));
 X=inv(C)*f

Any help will be appreciate

Answer 1

[Walter Roberson]

Example (untested)

pw = feval(symengine, 'piecewise', '([x < 0 or x > 1, 0], [x >= 0 and x <= 1, 1])');