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+function y = vco(x,frange,fs)
+//Voltage Controlled Oscillator
+//Calling Sequence
+//y=vco(x,fc,fs)
+//y=vco(x,[fmin fmax],fs)
+//Parameters
+//x
+//A vector or a matrix
+//fc
+//Carrier frequency
+//fs
+//fmin
+//Minimum frequency of the frequency range
+//fmax
+//Maximum frequency of the frequency range
+//Description
+//y=vco(x,fc,fs)
+//Creates a frequency modulated cosine wave y whose frequency varies as the magnitude of x
+//x lies in [-1,1]. x=-1 corresponds to a frequency of 0, x=0 corresponds to a frequency of fc 
+//and x=1 corresponds to a frequency of 2fc.
+//y=vco(x,[fmin fmax],fs)
+//Scales the frequency range so that x=-1 corresponds to a frequency of fmin and 
+//x=1 corresponds to a frequency of fmax
+//If x is a matrix the same operation is performed on the columns on x
+//Size of y is the same as the size of x
+//Example
+//x=rand()
+// x  =
+// 
+//    0.2113249  
+// y=vco(x,2000,8000)
+// y  =
+// 
+//    0.9454092 
+//Author
+//Ankur Mallick
+    funcprot(0);
+    if (argn(2)<3|argn(2)>5) then
+        error('Incorrect number of input arguments.');
+    else
+        if(argn(2)<3)
+            fs=1;
+        end
+        if(argn(2)<2)
+            fc=fs/4;
+            frange=fc;
+        end
+        if(max(abs(x(:)))>1)
+            error('x must lie between -1 and 1');
+        end
+        if(length(frange)==1)
+            fc = frange(1);
+            opt = (fc/fs)*2*%pi;
+        else
+            fc = mean(frange);
+            opt = (frange(2) - fc)/fs*2*%pi;
+        end
+        if (fc>fs/2)
+            error('The career frequency must be less than half the sampling frequency.')
+        else
+            y = modulate(x,fc,fs,'fm',opt);
+        end
+    end
+endfunction