how to write an equation with different period of time

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.

Answer 1

[Tomas]

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.

[Abdulelah]

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.

Answer 2

[Walter Roberson]

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.

[Abdulelah]

what should I define t and idx because I got error .

[Walter Roberson]

What error did you get?

The "t" for this should be the "t" or which you want the values to be calculated -- the "t" of the w(t) your equation defines.

You do not define "idx": it is calculated on lines 2, 4, and 6.

[Abdulelah]

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]

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))

Answer 3

[Amit]

w_t = [25*T 50 250-50*t];
t_range = [0 2 4];
W = w_t(find(t > t_range,1,'last'));

[Abdulelah]

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.