error using global parameter, to save value of parameter

hi,

how can i resolve this error; Global declaration not resolved to a Data Store Memory block registered via the Ports and Data Manager.

my code is:

function [y1, y2] = fcn(u)

%#codegen
coder.extrinsic('degtorad');

coder.extrinsic('radtodeg');

coder.varsize('Az','El','In','Or');

global k

Az=0;

El=0;

In=0;

Or=0;

n=0;

%k=0;

y1=0;

y2=0;

Azk =degtorad( u(1));

Elk= degtorad(u(2));

Ink=degtorad(u(3));

Ork=degtorad(u(4));

Az = [Az ; Azk];

El= [El ; Elk];

In=[In; Ink];

Or=[Or; Ork];

n=size(Az,1);

if (n==1)

k=1;

end

X2=cos(El(n))*cos(Az(n));

X3=sin(Az(n))*cos(El(n));

I=cos(In(k))*sin(El(n))-sin(In(n))*X2*cos(Or(k))-sin(In(k))*X3*sin(Or(k));

    if (0.9<I && I<=1)

      y1=radtodeg(In(k));

      y2=radtodeg(Or(k));

    else 

        if (n>1)

         k=n-1; 

   I=cos(In(k))*sin(El(n))-sin(In(n))*X2*cos(Or(k))-sin(In(k))*X3*sin(Or(k));

       y1=radtodeg(In(k));

      y2=radtodeg(Or(k));

        end

end

[Walter Roberson]

Merged into existing question http://uk.mathworks.com/matlabcentral/answers/219737-error-using-global-to-save-value-of-parameter