Why do I get "Array indices must be positive integers or logical values"?

clc

clear

R=1;

C=1;

vf=18;

ti=0;

tf=10;

h=0.5;

tao=R*C;

t=ti:h:tf;

vt=vf(1-exp(-t/tao));

tabla=[t' vt']

Answer 1

[Star Strider]

MATLAB does not recognise implicit multiplication, so the missing multiplication operator

vt=vf(1-exp(-t/tao));

↑ ← HERE

causes MATLAB to treat the contents of the parentheses as an array index, throwing the error.

This now works —

R=1;
C=1;
vf=18;
ti=0;
tf=10;
h=0.5;
tao=R*C;
t=ti:h:tf;
vt=vf*(1-exp(-t/tao));
tabla=[t' vt']

tabla = 21×2

0 0 0.5000 7.0824 1.0000 11.3782 1.5000 13.9837 2.0000 15.5640 2.5000 16.5225 3.0000 17.1038 3.5000 17.4564 4.0000 17.6703 4.5000 17.8000

.

Answer 2

[Dave B]

You're getting this message because of the line:

vt=vf(1-exp(-t/tao));

vf is the number 18, or, more precisely it's a matrix of size 1,1 which contains the number 18. This syntax is interpeted as trying to take the value of vt in the index 1-exp(-t/tao), so if vt was [5 9 1] and you wrote vt(2), it would return 9. What do you want to accomplish in this line? If it's multiplication...

vt=vf*(1-exp(-t/tao));