Proper way to use exist function.
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Jesse Crotts
am 9 Dez. 2018
Bearbeitet: Stephen23
am 9 Dez. 2018
I am using the ode23 function to call another function. The problem is that I need to change the time value each time the function is called in order to change another variable. Here is the part of the function that is not working to count time:
function f = wdotz(t,w,M,K,Q)
% -------------------------------------------------------
% time counter
AKA = exists(i);
if AKA == 0
i = 0
end
i = i+1;
time = (0:.001:22.5)';
treal = time(i);
% -------------------------------------------------------
when I run the code that calls this function it gives me this error:
Error: File: wdotz.m Line: 7 Column: 5
"i" previously appeared to be used as a function or command, conflicting with its use here as the name of a variable.
A possible cause of this error is that you forgot to initialize the variable, or you have initialized it implicitly
using load or eval.
2 Kommentare
Stephen23
am 9 Dez. 2018
Bearbeitet: Stephen23
am 9 Dez. 2018
"Proper way to use exist function."
I would argue that the "proper" way to use exist on a variable is to NOT use it: introspective programming is inherently inefficient, which is why experienced users and the MATLAB documentation warn against using it: "Avoid functions that query the state of MATLAB such as inputname, which, whos, exist(var), and dbstack. Run-time introspection is computationally expensive."
In any case, it is not clear what you expect your code to do. Please explain the expected behavior.
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Image Analyst
am 9 Dez. 2018
In your main, calling code, you do this:
f = wdotz(t,w,M,K,Q)
Note that none of the variables is called i. So there is never ever any i in your code, until you assign it.
exists() is not a function, but exist() is, and you'd need to pass in a second argument of 'var':
iExists = exist(i, 'var')
time() is a built-in function so don't use that as a variable name.
You're passing in t, which is perhaps a "time so far". If you're trying to return the elapsed time since t just do this
f = toc(t);
and get rid of everything else except the function line.
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Walter Roberson
am 9 Dez. 2018
The time value is being received into t and the ode routines will modify it as necessary to achieve integration tolerances.
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