I am not understanding how to resolve this issue.

I understand the error message you are encountering indicates that there is an issue on line 39 of the script Horsepool_DielCycle_v2, which is calling the function “sun_position” with the variables time and location as inputs. The error does not specify what the issue is, hence need to consider several possibilities.

Here are workarounds to check the error:

Check Function Availability: Make sure that the sun_position function is available in the MATLAB path. It might be a custom function or part of a toolbox one needs to install or add to the MATLAB path using the “addpath” function.
Inspect Input Variables: Verify that the variables time and location are correctly defined and formatted before being passed to the “sun_position function”. The time variable should typically be a datetime or date vector, and location should contain the necessary fields (such as latitude and longitude) expected by the function.
Function Definition: Look at the definition of the sun_position function to understand what inputs it expects and what outputs it provides. Make sure to use the function correctly according to its documentation.
Error Details: If there is more to the error message, read it carefully for clues. MATLAB often provides additional information about what went wrong, such as "Undefined function 'sun_position' for input arguments of type 'double'."
Check for Typos: Ensure there are no typos in the function name or the variable names.
Run the Function Separately: Try running the “sun_position” function with hard-coded inputs in the Command Window to see if it works outside of the script. This can help isolate whether the problem is with the function itself or how it is being used in the script.
Consult Documentation: If “sun_position” is part of a specialized toolbox or a third-party function, consult the relevant documentation or help files to ensure its usage.
Debugging: Use MATLAB's debugging tools to step through the script and inspect the variables just before the error occurs. Set a breakpoint on line 39, run the script, and when it pauses, check the current state of time and location.

If still the problem persists, consider providing more information and if sun_position is a custom function, review its code to ensure its functioning as expected.

Please refer to the documentation link:

https://in.mathworks.com/help/matlab/ref/addpath.html?searchHighlight=addpath&s_tid=srchtitle_support_results_1_addpath

Hope it helps!

Best Regards,  

Simar  