how to pass parameters in arx function for MISO system identification

This is my code for an estimation of a MISO system:

na= 1;
nb1=1;
nb2=1;
sampleTime = 300; % seconds

inputNames = ["HCL_in", "NaHCO3"];
outputName = "HCL_out";

data = iddata(Dati1_timetable{:,outputName}, Dati1_timetable{:, inputNames}, sampleTime);
sys5 = arx(data, [na nb1 nb2]) 

and I have this error :

Error using arx (line 84)

the model orders must be compatible with the input an output dimensions of the estimation data.

if I substitute ONLY " inputNames = ["HCL_in", "NaHCO3"]; " with this: " inputNames = HCL_in; " , so from MISO to SISO system identification, all works fine.

Please help me, thanks.

[jefferson]

Where can I get theoretical information for implementing a MISO system? I need to solve a case similar to this.

Answer 1

[Giovanni Barba Orsato]

Solved, unlike the theory books where it is specified by the relative degrees, it is necessary to specify the delay for each input. In my case, it is 0 due to very slow sampling time, so I solved it with:

na= 1;
nb1=1;
nb2=1;
nk1=0;
nk2=0;
sampleTime = 300; % seconds
inputNames = ["input_1_name", "input_2_name"];
outputName = "output_name";
data = iddata(Dati1_timetable{:,outputName}, Dati1_timetable{:, inputNames}, sampleTime);
sys5 = arx(data, [na nb1 nb2 nk1 nk2])