What does this mean? (Attempted to access Q(0); index must be a positive integer or logical.)

I am trying to use the formula Q(t ) = CV(1 − e−t/RC ) to monitor the charge on the capacitor every .2 seconds given V = 9,R = 4, C = 1, and Q at t(0) = 0. We are supposed to display the time and charge every .1 seconds until Q exceeds 8.

This is my code so far:

Q(0)=0;

V = 9; %Voltage

R = 4; %Resistor Value

C = 1; %Capacitor Value

p = 0;

t = .1; %Time

for Q = 0:8

    Q(t) = C * V * (1-exp(-(p+t)/(R * C)));     %Charge Function

    plot (Q(t),'c+')

end

When I attempt to evaluate the code i keep getting this:

Attempted to access Q(0); index must be a positive integer or logical.

Thank you

Answer 1

[Azzi Abdelmalek]

In Matlab you can not use

A(0) or A(-1) or A(1.5)

index must be a positive integer or logical:

Positive integer are: 1,2,3,...

Logical are: logical(0) and logical(1)

[Turk]

now when I change the Q(0) to Q(1) I get:

>> Q(1)=0;

V = 9; %Voltage

R = 4; %Resistor Value

C = 1; %Capacitor Value

p = 0;

t = .1; %Time

for Q = 0:8

    Q(t) = C * V * (1-exp(-(p+t)/(R * C)));     %Charge Function

    plot (Q(t),'c+')

end

Attempted to access Q(0.1); index must be a positive integer or logical.

How would you correct this? I am not that good at Matlab yet sadly..

[Azzi Abdelmalek]

Yes, you can not use Q(0.1) because 0.1 is not positive integer

Answer 2

[Daniel Shub]

Your for loop doesn't make any sense. It is a bad idea to iterate on a variable that you then change within a for loop (in this case Q). Further, t is a non-integer value so cannot be used to index Q. Finally plot (Q(t),'c+') is probably not doing what you expect.

MATLAB comes with some really great documentation. I suggest reading it.