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

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Turk
Turk 2013-3-10
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

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回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-3-10
编辑：Azzi Abdelmalek 2013-3-10
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)
  2 个评论
Turk
Turk 2013-3-10
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..

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Daniel Shub
Daniel Shub 2013-3-10
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.

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