ATLAB Lecture 5 School of Mathematical Sciences Xiamen University http∥gdjpkc.xmu.edu.cr To determine what symbolic variables are present in an expression, use the findsym >>ffxn: gg=sin(a*t+btc): %given the symbolic expressions f and g > findsym(ff) %find the symbolic variables in ff > findsym(gg) %find the symbolic variables in gg b t 2 * Creating Abstract function >>f=sym(f(x)) % create an abstract (i. e, indeterminate)function Then f acts like and can be manipulated by the toolbox command df=(subs(f, x', x+h")-fh %to construct the first difference x h > df=(subs(f,x, x+h)-f/h df This application of sym is useful when computing Fourier, Laplace, and Z-transformsMATLAB Lecture 5  School of Mathematical Sciences Xiamen University  http://gdjpkc.xmu.edu.cn  Lec5­9  To determine what  symbolic variables  are present  in  an expression,  use the findsym  command.  >> syms a b n t x z  >> c=1  >> ff= x^n; gg = sin(a*t + b+c);  %given the symbolic expressions f and g  >> findsym(ff) %find the symbolic variables in ff ans =  n, x  >> findsym(gg) %find the symbolic variables in gg  ans =  a, b, t  ² *Creating Abstract Functions >> f = sym('f(x)') % create an abstract (i.e., indeterminate) function  Then f acts like and can be manipulated by the toolbox commands.  >> df = (subs(f,'x','x+h') ­ f)/'h'  %to construct the first difference ratio  or >> syms x h  >> df = (subs(f,x,x+h)­f)/h  df =  (f(x+h)­f(x))/h  This application of sym is useful when computing Fourier, Laplace, and z­transforms