@Christian Berwanger: the line
exist('Nodes','var')==0
checks if Nodes exists in the workspace where that code is run. The line
assignin('base','Nodes',Nodes);
defines a variable called Nodes in the base workspace. There are two likely scenarios:
1. your code is in a function: then each time the function is called Nodes will be undefined in the function workspace and so the file will be loaded again.
2. you are running that code in a script called from the base workspace: then assignin is totally superfluous.
So both of these scenarios are flawed.
You could resolve the first scenario by using evalin. But I would suggest that this approach is flawed as well: it will work, but it is the kind of approach that beginners use to write slow, complex, inefficient code. Beginners love spamming all of their variables into the base workspace, and get some feeling of security from looking at all of those lovely variables sitting in the Variable Viewer pane. I know, I can remember that feeling!
But relying on the base workspace is a bad way to write code. Spamming variables into the base workspace is slow and is risky (e.g. overwriting variables without warning). Those beginners also typically try to write functions that magically access the variables in the base workspace (as you are trying to do) and perform some operations on them, but all of the techniques that can achieve this are slow, complex, inefficient, and will increase the chance of bugs. For example, introspective coding (e.g. exist) is slower than simply checking for an empty array or using nargin. On top of that, calling exist in different workspace is slower still, because any magical jumping between workspace will slow your code down (conversion to string, removes JIT code acceleration, etc).
Basically your entire approach forces you to write slow, complex, inefficient code.
If you want to write simpler, neater, efficient MATLAB code then forget about magically running things in other workspaces and magically checking if something exists somewhere else or not. Also, forget about the base workspace. Simply write functions, and pass all values as input and output arguments. Checking those arguments is easy. It will also be very efficient. This is the first step to learning how to write simple, reliable code. Functions are how experienced users write reliable, efficient, testable, robust code.
See my answer for a simpler, neater, more efficient solution.
PS: you might like to read this:
