MATLAB: Constants and Matlab Workspace

MATLABworkspace

Say I have defined X1 = 20 in a script file and ran the script file. So my Workspace has X1=20.

I open up Simulink and create a model where I create a condition. I compare a new variable X2 (X2 = 40) to X1 in Simulink, and if X2 > X1, then set X1 = 40. I noticed that X1 appears to change to 40 in Simulink but not in the Workspace. Why is that?

So what is the actual value of X1 in Matlab? is it 20 or 40 then? or maybe Im not doing something correctly here?

Best Answer

The MATLAB has several different workspaces. Simulink model has its own workspace: https://www.mathworks.com/help/simulink/ug/using-model-workspaces.html. The workspace you see on the main MATLAB window is called the base workspace. The method to change a variable in base workspace depends on what you are trying to do. One way is to use the To Workspace block: https://www.mathworks.com/help/simulink/slref/toworkspace.html. The other is to use evalin and assignin functions, as shown in the attached file. To run this model, define a variable x in the base workspace by running

x = 5

Then run the model. In the Simulink model, there is a MATLAB function block, which increments the value of x at each time instant. However, note that using evalin and assignin is not a recommended practice, and they can make the model run very slow. If possible, try using the To Workspace block as it will not result in slow performance.

Related Solutions

MATLAB: Variable in local function in livescript

The variable a is defined in base workspace and hence, the error is because of the unavailability of variable a in function workspace. To share the data from base workspace with function workspace, you may make the variable a global.

global a
a = 1;

You also need to declare a as global in the function

function y = multi(x)
global a
y = a*x;
end

You may refer the following documentation for different practices of sharing data between workspaces

https://in.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

You may refer the following docmentation for differences between base and function workspace

https://in.mathworks.com/help/matlab/matlab_prog/base-and-function-workspaces.html

MATLAB: How to declare a variable in the MATLAB workspace from a MATLAB function

Simulink has access to any variable defined in the MATLAB workspace. You do not need to declare a variable 'global'. In order to define a variable in the MATLAB workspace from a function, you can declare the variables in the function using the command EVALIN. For example:

function declare_variable
......
evalin('base','k=100');
......

In this example, when the function 'declare_variable' is called, it will generate a variable 'k' in the MATLAB workspace. This variable can then be seen by the Simulink model. Please note that if, before the function 'declare_variable' is called, a variable called 'k' exists in the MATLAB workspace already, calling the function 'declare_variable' will overwrite the existing variable 'k' with the new value (100).

For more information on the EVALIN function, see the following URL:

http://www.mathworks.com/access/helpdesk/help/techdoc/ref/evalin.html?cmdname=evalin

Best Answer

Related Solutions

MATLAB: Variable in local function in livescript

MATLAB: How to declare a variable in the MATLAB workspace from a MATLAB function

Related Question