how to write an equation with different period of time

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Abdulelah
Abdulelah 2014-2-3
编辑： per isakson 2017-9-17
how can I writ this equation in matlab.
25*t 0<= t <= 2
W(t)= 50 2<= t <= 4
-05t+250 4<= t <=5
thank for everyone trying to help.

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回答（3 个）

Tomas
Tomas 2014-2-3
编辑：Tomas 2014-2-3
I can think of two ways, one is using a "for" and ifs and its not very efficient but it will get it done like this:
t=0:0.1:5
for i=1:length(t)
if t(i)>=0 &&t(i)<=2
w(i)=25*t;
elseif t>=2 && t<=4
w(i)=50;
elseif t>=5 && t<=5
w(i)=-5*t+250;
end
end
The other one is harder to explain. I hope this is enough.
  1 个评论
Abdulelah
Abdulelah 2014-2-3
thank you unfortunately it doesn't work with me.
I got this message. In an assignment A(I) = B, the number of elements in B and I must be the same.

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Walter Roberson
Walter Roberson 2014-2-3
w = nan(size(t));
idx = 0 <= t & t= < 2;
w(idx) = t(idx) * 25;
idx = 2 <= t & t <= 4;
w(idx) = 50;
idx = 4 <= t & t <= 5;
w(idx) = 250 - 50 * t;
Notice that this leaves undefined (NaN) any position for which t < 0 or t > 5.
You double-define the values at 2 exactly and 4 exactly but the two definitions have the same value at the exact boundary so there is no discontinuity.
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Abdulelah
Abdulelah 2014-2-4
first I got this
EDU>> w = nan(size(t));
Undefined function or variable 't'.
second error is
EDU>> idx = 0 <= t & t= <2;
idx = 0 <= t & t= <2;
Error: The expression to the left of the equals sign is not a valid target for an assignment.
Walter Roberson
Walter Roberson 2014-2-4
编辑：per isakson 2017-9-17
function r = w(t)
r = nan(size(t));
idx = 0 <= t & t= < 2;
r(idx) = t(idx) * 25;
idx = 2 <= t & t <= 4;
r(idx) = 50;
idx = 4 <= t & t <= 5;
r(idx) = 250 - 50 * t;
end
The above defines an equation named "w" that takes a parameter on input and returns the value according to your definition.
This is what you asked, to define the equation.
You can use the equation like any MATLAB function, by calling its name and passing in the value you want to process. For example,
T = -10:.01:10;
plot(T, w(T))

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Amit
Amit 2014-2-3
w_t = [25*T 50 250-50*t];
t_range = [0 2 4];
W = w_t(find(t > t_range,1,'last'));
  1 个评论
Abdulelah
Abdulelah 2014-2-4
Thank you, but I got this message
EDU>> t = 0:0.1:5;
EDU>> w_t= [25*t 50 250-50*t];
EDU>> t_range = [0 2 4];
EDU>> W = w_t(find(t > t_range,'last'));
Error using >
Matrix dimensions must agree.

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