What does this error " Undefined operator '*' for input arguments of type 'string' " means?

I have this code (part of a script)

    for i=1:N
                Size = Event_List(1,4);  
                Start_trans_time_ONU(i) = CurrentTime + (Distances(i) /   Prop_speed) + Size * 8/ (C *(10^9));
                End_Trans_time_ONU(i) = Start_trans_time_ONU(i) +  (Distances(i)/Prop_speed) + Grant_time;
                aux = End_Trans_time_ONU(i) + Guard_time;
                Trans_ONU = i+1;
                Event_List = [Event_List; DepartureONU aux 0 0 i+1];
             end

And I get the error "Undefined operator '*' for input arguments of type 'string'" on 3rd line.

Can anyone help me on solving it?

Many thanks in advance.

[Bob Thompson]

What type of variables are 'C' and 'Size'?

[Aziza Zaouga]

C and Size are nmbers. The problem is in 'Size'. I don't know why it considering it as a string and even when I tried to convert it to an integer, the problem still exist.

[Bob Thompson]

Ok, so what is Event_List(1,4) then? What type of array is eventlist?

[Aziza Zaouga]

I wrote Event_List(1,4) to be a double but I figured out that I added a field which is a string. So all variables in Event_List became string. I changed that field and it worked. Anyway, many thanks for your help :)

Answer 1

[Jan]

The error message is clear: In the failing line you try to multiply a string, but this is not meaningful.

You know that the problem occurs in this line:

Start_trans_time_ONU(i) = CurrentTime + (Distances(i) / Prop_speed) + ...
                          Size * 8 / (C *(10^9));

Then use the debugger to find out, where the problem is: Debugger. Eitehr set a breakpoint in this line or type this in the command window:

dbstop if error

Now run the code until Matlab stops at the named line. You can examine the values of the variables, e.g.:

class(Size)
class(C)

One of them is a variable of class string and a multiplication is meaningless. Convert it to a number.

By the way: 10^9 is an expensive power operation, which is evaluated in each iteration, while 1e9 is a cheap constant.

[Aziza Zaouga]

Thank you a lot for helping.