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Using For loop to change array values in simulink stateflow

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Hello, my model is generally about a mobile charging station where a robot picks up a battery from the charge station and drives it a particular car, charges the car and returns the battery to the station
My stateflow model has an input vector called batLevel (carrying the state of charge for four different batteries) gotten from Simulink using the "vector concatenate" block. I appleid a graphical for loop function (pickBat which has input as batLevel) to check the values of the batLevel vector. If batLevel(i) == 100 then battery i should be disconnected from charge station by setting charge(i) = 0 (charge is a output varriable which indicates if the battery is charging (-1), idle (0), or discharging (1)) and picked up by setting bat(i) = 1 (bat is a data variable which indicates if the robot has pickedup bat(i) or not). charge and bat are both 1xm vectors like batLevel. I called my graphical function before a battery is to be picked up from the charge station and for the other transitions, I used batLevel(i), bat(i) and charge(i) to refer to the active battery. Unfortunately, i get the error "Subscript indices must either be real positive integers or logicals." and batLevel(i) is coloured red.
1) I would like to know if using the for loop is a good option
2) if it is, then why am i having this error and how can I solve it
Attached is a picture of the for loop implementation and the substate where it is called
Thanks in advance for your reply and if further clarification is needed, i will not mind adding some stuff

Accepted Answer

Scott Satinover
Scott Satinover on 1 Jul 2021
Hi Kizito, it looks like your main problem comes from the function you made. Try incorporating these solutions:
  1. The function you've created, pickBat, doesn't have any output arguments, so it won't return anything. Make sure pickBat outputs something (ie [out1, out2,... ,outn] = pickBat(arg1, arg2,... ,argn)). For this function, you'll want pickBat to output the new values for charge and bat. When you call the function, also make sure to include output arguments.
  2. Currently you're not looping over the index. You're working with only the first index of the input vector, so the vector never properly outputs. You need to incorporate a for loop by introducing the condition i < length(charge) into the function chart, and then you need to check that each index is equal to 100. In matlab code, think of it as an if statement inside of a for loop. You can do this by combining the patterns provided in the pattern wizard. Or you can always write the function in MATLAB code with the MATLAB function in the chart (not to be confused with the Function you're using!). https://www.mathworks.com/help/stateflow/ug/programming-a-matlab-function-in-a-chart.html
As a sign of caution, be considerate of the variables here. Stateflow charts don't handle duplicate variables well. This may require some rewording of the commands. Hopefully this steers you in the right direction.
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