Attempt to extract field 'pmv' from 'mxArray'

Hello,

I am trying to create a MATLAB fuction for calculating PMV using already created Python Library. This function is being called into a simulink model. The code is as follows for custom simulink block:-

function [pmvf,ppdf] = PMV_BLOCK(tdb, tr, vr, rh, met, clo)
pmvf=0;
ppdf=0;
tr = 25;
tdb= 25;
rh = 50;
v = 0.1;
met = 1.3;
clo = 0.8;
coder.extrinsic('py.pythermalcomfort.utilities.v_relative');
v_r=py.pythermalcomfort.utilities.v_relative(v, met); %to calculate relative velocity from absolute velocity
coder.extrinsic('py.pythermalcomfort.utilities.clo_dynamic');
clo_d=py.pythermalcomfort.utilities.clo_dynamic(clo, met); %to calculate clothing insulation
coder.extrinsic('py.pythermalcomfort.pmv_ppd');
pmvx=py.pythermalcomfort.pmv_ppd(tdb, tr, v_r, rh, met, clo_d); %to calculate pmv and ppd
l=struct(pmvx);
pmvx.pmv

Whenevever i tries to run the matlab function block (via simulink model run), i get the following error message:-

Error :-

"Attempt to extract field 'pmv' from 'mxArray'. Function 'PMV Calculator' (#172.613.617), line 17, column 1: "pmvx" Launch diagnostic report."

Even after checking multiple websites no solution could be traced. My project requires me to calculate pmv through matlab function only (when called from Simulink run).

Any quick suggestion on how to extract values from mxarray in the matlab function block?

Thanks in advance.

Answer 1

[Walter Roberson]

pmvx=py.pythermalcomfort.pmv_ppd(tdb, tr, v_r, rh, met, clo_d); %to calculate pmv and ppd

As far as Simulink knows, the result of that call is going to be numeric of some size or other. And then you try to extract a field from what is assumed to be numeric.

You need to first assign pmvx as a struct array with the same fields (in the same order) as py.pythermalcomfort.pmv_ppd will return. Then you assign pmvx as the result of that calls.

pmvx = struct('pmvorder', [], 'pmvx', [], 'pmvsmooth', [], 'pmvy', []);
pmvx = py.pythermalcomfort.pmv_ppd(tdb, tr, v_r, rh, met, clo_d); %to calculate pmv and ppd

except that the field names and orders have to match the real return value.

[Shray]

i tries to use your suggestion, plese check here:-

function pmvf  = PMV_BLOCK(tdb, tr, vr, rh, met, clo)
pmvf=0;
ppdf=0;
%pmvx=0;
tr = 25;
tdb= 25;
rh = 50;
v = 0.1;
met = 1.3;
clo = 0.8;
%l=[0 0];
coder.extrinsic('py.pythermalcomfort.utilities.v_relative');
v_r=double(py.pythermalcomfort.utilities.v_relative(v, met)); %to calculate relative velocity from absolute velocity
coder.extrinsic('py.pythermalcomfort.utilities.clo_dynamic');
clo_d=double(py.pythermalcomfort.utilities.clo_dynamic(clo, met)); %to calculate clothing insulation
coder.extrinsic('py.pythermalcomfort.pmv_ppd');
pmvx= struct('pmv', [], 'ppd', []);
pmvx=py.pythermalcomfort.pmv_ppd(tdb, tr, v_r, rh, met, clo_d) %to calculate pmv and ppd
coder.extrinsic('py.list');
coder.extrinsic('keys', 'values');
keys(pmvx);

As shown here just before the pmvx=py.pythermalcomfort.pmv_ppd(tdb, tr, v_r, rh, met, clo_d) i used struct function as suggested by you. But now i am gettingmthe following error:-

An error occurred while running the simulation and the simulation was terminated

Caused by:

• MATLAB expression '<output of py.pythermalcomfort.pmv_ppd>' is not of the correct class: expected 'struct', found 'py.dict'.

What should be done now???

[Shray]

Even after declaring struct as an extrinsic function i am not able to extract values from pmvx? My original question still persists how to extract values from maxarray?

Thanks in advance

[Walter Roberson]

Ah, so then instead of

pmvx= struct('pmv', [], 'ppd', []);

you need to initialize it as a py.dict (somehow)