How can I add a constant to a variable during a simulation in Simulink?

I want to make the percentage of one variable. The operation is (initial value - final value)/ initial value. The initial value is a constant (2.646) and the final value is changing over time. I have performed the calculation with blocks shown below, but it cannot be solved because initial value is a constannt and final value changes over time.

So my question is, how can I make this operation in Simulink?

Thanks

Answer 1

[Mathieu NOE]

hello

I had no particular problem doing the same simulink model and running it . what is your issue ??

NB : you post that the initial value is a constant (2.646) and in your simulink model is 0.2646.

attached my model fyi

the variable (final) value is a sinus of amplitude 1

the plot shows that this generates a variation of +/- 40 % around 100%

[Marta Costa de Aguirre]

Hello,

Yes, there was a mistake in my typing. The constant value is 0.2646.

Thanks for your answer but I still cannot run it. It gives me this error: Invalid matrix variable specified as workspace input in 'DosageAllCodesnewklak6k8/[Ci]0 Initial concentration of component i inside the reactor, mmol//L/From Workspace3'. The matrix data must be a real, double, have two dimensions, and at least two columns. The first column must contain time values and the remaining columns the data values. Matrix values cannot be Inf or NaN.

I think my problem is with out.TOCb. It is a vector 189x1 and Simulink wants it with the time, so its dimension should be 189x2. So, how can I get out.TOCb as 189x2?

Should I change something in 'To Workpace'?

[Mathieu NOE]

hello

I don't think we have a problem with out.TOCb because this is a "To Worspace" block

your error message deals with a "From Worspace" block.

'DosageAllCodesnewklak6k8/[Ci]0 Initial concentration of component i inside the reactor, mmol//L/From Workspace3'.

This block needs to be initialized with a 2 column array (time and data)

The faulty block should be highlighted in yellow in you simulink file