??? Undefined function or method 'sign' for input arguments of type 'sym'.

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abhijit kulkarni
abhijit kulkarni 2013-8-25
I am trying to generate a wave :
when time=0:5 then r(t)=1
when time=5:10 then r(t)=2
when time=10:15 then r(t)=1
and then I also want to take derivative of this wave (even double derivative also)
I tried it without giving t=0:15 and with syms
code:
t= 0:0.1:14.9;
aaa=sin(2*pi*0.1*t');
% %r = [1,zeros(120,1)]+2-sign(aaa);
r =2.000-sign(aaa);
size(r)
r1=diff(r,t);
size(r1)
rp=horzcat(0,r1);
size(rp)
size(t)
plot(t',rp)
------
error:when time=0:5 then r(t)=1
I also tried with if loop ,
if t>=0 && t<=5
r=1;
if t>=5 && t<=10
r=2;
if t>=10 && t<=15
r=1;
this aslo doesnot work; give some logical error message
please help

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采纳的回答

Walter Roberson
Walter Roberson 2013-8-25
"when" is not a MATLAB or MuPAD command.
Your code does not use sym() or syms, so you could not be getting an error about sign of sym.
Your "t" is a vector, so "t>=0" is a vector result as is "t<=5". You cannot join vector results with "&&" as "&&" is reserved for scalars. You need to use "&" to join vector results. But you should probably read the definition of how "if" works carefully

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