Persistent Variable will not update in a function call

I have a sub-function of an EML Simulink Block that has a persistent variable, wm_last, declared. The variable is not used anywhere other than within this function call. I keep getting an error when I try to update this variable. When he line, "wm_last = wm" is uncommented, my model will not build. What gives?

function  corr = LeverArmCorrection(m_deltaTime, deltaThetaMountingFrame, ...
          earthRateMountingFrame)

        persistent wm_last
        if isempty(wm_last)
            wm_last = zeros(1,3);
        end

        m_TableLeverArm      = [0.00524;  0.4416;  1.2755];

        %mounting to ENA frame rate (rad/sec)
        wm = (deltaThetaMountingFrame / m_deltaTime) - earthRateMountingFrame;

         %mounting to ENA frame angular acceleration (rad/sec^2)
        am = (wm - wm_last) ./ m_deltaTime;

     %      wm_last = wm;

        %mounting frame sensed acceleration sensitivity to lever arm
        XM  = zeros(3,3);   % mounting frame sensed accel sensitivity to lever arm (ft/sec^2/ft)
        XM(1, 1) = -wm(2).^2 - wm(3).^2;
        XM(2, 2) = -wm(1).^2 - wm(3).^2;
        XM(3, 3) = -wm(1).^2 - wm(2).^2;

        XM(1, 2) = wm(1) * wm(2) - am(3);
        XM(1, 3) = wm(1) * wm(3) + am(2);
        XM(2, 1) = wm(2) * wm(1) + am(3);
        XM(2, 3) = wm(2) * wm(3) - am(1);
        XM(3, 1) = wm(3) * wm(1) - am(2);
        XM(3, 2) = wm(3) * wm(2) + am(1);

       %lever arm correction (ft/sec^2)
        XRM  = (XM * m_TableLeverArm)';

        corr =  XRM .* m_deltaTime;
  end

[Sebastian Castro]

What's the error you're getting?

[Alyssa]

I get an "Error occured during pasring of Matlab Funciton 'GCA/Local/..."

If I comment out the "wm_last = wm" as shown above, the model compiles and runs just fine. Error doesn't give you much, does it...

Answer 1

[Image Analyst]

Try making it global instead of persistent. It should work then.

[Stephen23]

@Image Analyst: Do you have any explanation of why presistent does not work? I can't see why it shouldn't.

[Image Analyst]

No I don't. Hoping to hear if this solved it. If no other functions declare the variable global then it's just in this function, and for all intents and purposes it's like a persistent except it's easier because you don't have to initialize it.

[Alyssa]

When I make the variable global, I get a port dimension error. I'm completely stumped. We have persistent variables in multiple other subfunctions - updated in exactly the same way. This makes no sense.

[Stephen23]

@Alyssa: can you please give us the complete error message, which includes all of the red text.