how we can define piecewise function in matlab?
显示 更早的评论
in maple we can use comamnd:(
f:= piecewise(0 <= t and t <= T1, f1, T1 < t and t < T2, 0, T2 <=t and t <= T3, f1, T3 < t and t < T4, 0)
but in matlab i can not define this function.
please give me som information ...
thanks
采纳的回答
Sally Al Khamees
2016-12-23
编辑：Sally Al Khamees
2017-2-21
2 个投票
If you have R2016b and the Symbolic Math Toolbox installed, you can just use the piecewise function:
更多回答（3 个）
Walter Roberson
2013-10-12
You cannot define that as a function in MATLAB. MATLAB functions need to have a defined value for the case where none of the conditions hold. If you were absolutely sure that one of the conditions will hold you would rewrite the Maple function without the final condition, as
piecewise(0 <= t and t <= T1, f1, T1 < t and t < T2, 0, T2 <=t and t <= T3, f1, 0)
This would be
function y = f(t, T1, T2, T3, f1)
y = zeros(size(t));
idx1 = 0 <= t & t <= T1;
y(idx1) = f1;
idx2 = T1 < t & t < T2;
y(idx2) = 0;
idx3 = T2 <= t & t <= T3;
y(idx3) = f1;
y(~(idx1 | idx2 | idx3)) = 0;
end
4 个评论
ebi
2013-10-12
hello dear walter... thanks for your answer , but i think i couldn't express clearly. i want define a piecewise function like as picture below that t is variable and we have f(t)= picture below and i want to plot it and do fourier illustration of it and use fft function on it ant plot them.
Walter Roberson
2013-10-12
You can only do fourier transforms symbolically, using the symbolic toolbox. For numeric values, you need to use fft (fast fourier transform) or the like.
If you want to use the symbolic toolbox to create the MuPAD equivalent of the Maple function, you need to change the syntax very slightly:
f_generic = sym('piecewise((0 <= t and t <= T1, f1), (T1 < t and t < T2, 0), (T2 <=t and t <= T3, f1), (T3 < t and t < T4, 0))');
Note: possibly the inner () should be [] instead.
Before using you would want to
f = subs(f_generic, {'T1', 'T2',, 'T3', 'f1'}, {0.02, 0.287, 0.307, 0.335});
Note that the result would be a symbolic formula, not a function. To get the function version, use
f_generic = sym('t -> piecewise((0 <= t and t <= T1, f1), (T1 < t and t < T2, 0), (T2 <=t and t <= T3, f1), (T3 < t and t < T4, 0))');
ebi
2013-10-12
Walter Roberson
2017-2-21
Note: my later experiments showed that using sym('t->...') cannot possibly create a symbolic function.
sixwwwwww
2013-10-12
Dear ebi, You need something like this if I understood correctly:
syms f f1
t = input('Enter value of t: ');
% Assuming values of T1, T2 and T3 as follows
T1 = 10;
T2 = 20;
T3 = 30;
if ((t >= 0 && t <= T1) || (t >= T2 && t <= T3))
f = f1; % here you can define f1 as you wish
else
f = 0;
end
Is it ok?
3 个评论
ebi
2013-10-12
hello dear sixww... thanks for your answer , but i think i couldn't express clearly. i want define a piecewise function like as picture below that t is variable and we have f(t)= piecewise function and i want to plot it and do fourier illustration of this function and use fft function on it ant plot them.
sixwwwwww
2013-10-12
Do you input 't' as a time vector? and get f(t) for which you can calculate fft? Is it right?
ebi
2013-10-13
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