Error: "Array indices must have positive or logical values"

close all;
clc;

Tp = .00005;
Bw = 10^8;
P = 1; %Watt
R = 10^3; %m
r = 20*10^9; %sps
t = linspace(0,Tp,(r.*Tp)); 
Fif = 10^9; %intermediate frequency
g = Bw./Tp; %chirp rate
a = 1; %rectangularPulse((t-.5.*Tp)./Tp);
Xif(t) = a.*cos(2*pi*(Fif-.5*Bw).*t + pi*g*t.^2); %g ="chirp rate"

figure;
plot(t,Xif(t));

That's my code, and I keep getting that error for some reason. I'm not sure how to fix it.

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Walter Roberson]

You are getting confused between formula and expressions.

When you define Xif(t) = something, you are probably thinking in terms of typical notation for defining a formula -- a statement that for some arbitrary t to be determined later, that what is on the right hand side defines how the value of Xif should be computed.

But in MATLAB, things do not work that way. I recently explained in the bottom half of https://www.mathworks.com/matlabcentral/answers/453312-matlab-error-array-indices-must-be-positive-or-logical-values#answer_368153