"Undefined function or variable 'PA'. The first assignment to a local variable determines its class.". Why do I keep getting this error?

I have a function for my MPPT which i will implement or arduino using simulink but whenever i try to run the simulation it shows me this error "Undefined function or variable 'PA'. The first assignment to a local variable determines its class."

function D= fcn(VA,IA)
persistent VAprev
persistent PAprev
persistent Dprev

if isempty(VAprev)
    VAprev = 0;
end 
if isempty(PAprev)
    PAprev = 0;
end
if isempty(Dprev)
    Dprev = 0.5;
end
dataType = 'double';
double(PA);
double(IA);
D=Dprev;
PA=VA*IA;
DeltaVA= VA-VAprev;
DeltaPA= PA-PAprev;
if DeltaPA>0
    if DeltaVA>0
        D=Dprev - 0.0001;
    elseif DeltaVA<0
        D=Dprev +0.0001;
    end
elseif DeltaPA<0
    if DeltaVA>0
        D=Dprev+0.0001;
    elseif DeltaVA<0
        D=Dprev-0.0001;
    end
end
if D>0.9
    D=0.9;
elseif D<0
    D=0;
end

VAprev=VA;
PAprev=PA;
Dprev=D;

Answer 1

[Walter Roberson]

double(PA);
double(IA);
D=Dprev;
PA=VA*IA;

You do something (useless) with PA before you assign to it.

Remember in MATLAB a type name used like a function is not a type declaration, it is a type conversion.

PA = 0;

might be suitable

[Ali Zubair]

i tried this,

PA = 0;

still same error.

[Walter Roberson]

function D = fcn(VA,IA)
    persistent VAprev
    persistent PAprev
    persistent Dprev
    
    if isempty(VAprev)
        VAprev = 0;
    end 
    if isempty(PAprev)
        PAprev = 0;
    end
    if isempty(Dprev)
        Dprev = 0.5;
    end
    
    D = 0;
    IA = 0;
    PA = 0;
    PV = 0;
    DeltaVA = 0;
    DeltaPA = 0;
    
    D = Dprev;
    PA = VA*IA;
    DeltaVA = VA-VAprev;
    DeltaPA = PA-PAprev;
    if DeltaPA>0
        if DeltaVA>0
            D = Dprev - 0.0001;
        elseif DeltaVA<0
            D = Dprev + 0.0001;
        end
    elseif DeltaPA<0
        if DeltaVA>0
            D = Dprev + 0.0001;
        elseif DeltaVA<0
            D = Dprev - 0.0001;
        end
    end
    if D>0.9
        D = 0.9;
    elseif D<0
        D = 0;
    end
    
    VAprev = VA;
    PAprev = PA;
    Dprev = D;
end