Question

Im a new MATLAB user. Trying to initialize y to the calculated value in the if statement. However, when I try to plot y it says y not defined

function [y,xmax] = Alaw(x,A,ymax)

if nargin<3, ymax=1; end
if nargin<2, A=87.6; end


xmax=max(abs(x)); 

    temp = ymax/A;
if ((x > 0) & ( x < temp ))
    y = (A * abs(x)) ./ (1 + log(A) ).*sign(x);
end    

if (x > temp)
    y = ymax*( 1 + log(A*abs(x/ymax)) )./( 1+log(A) ).*sign(x);
end


 fprintf('Plotting Data ...\n');
 hold on;
 figure;
 plot(y);
 xlabel('x-axis');
 ylabel('y-axis');
 title('  A LAW ');

 pause;
 fprintf('Writing the audio file ...\n');
 wavwrite(y, 22050, 'Alaw.wav');


 end

Answer 1

If x is smaller than or equal to zero, or if x equals temp, neither of the if-statements is true, and thus, y never gets defined. You may want to re-write the logic with if..elseif..else to ensure that y gets assigned in every case:

if ((x > 0) & ( x < temp ))
    y = (A * abs(x)) ./ (1 + log(A) ).*sign(x);
elseif (x > temp)
    y = ymax*( 1 + log(A*abs(x/ymax)) )./( 1+log(A) ).*sign(x);
else
    y = NaN(size(x)); % no valid y; this won't plot anything, but won't error
end

Note that x>0 can lead to unexpected results when x is an array. Use all or any to make sure that the condition is satisfied if either all or any of the elements of x satisfy the condition, respectively.