Rotate a set of 2D coordinates about the origin

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Rotates a set of 2D coordinates about the origin. Written for counterclockwise rotation so that last coordinate in a 2D wave is moved to y=0.
2D waves are organized with x cordinates in first column y coordinates in second column.
To move to a different position ABx ABy and the if-else-endif statements need to be changed.

Function Rotator(wavenames) //Select top graph. Execute with rotator(wavelist("*",";","WIN:"))
	String wavenames
	Variable theta, xprime, yprime, xcd, ycd
	variable i=0
	Variable j=0 // i will count through the waves, j will be row index
	Variable ABx, CDx, ABy, CDy
	For (i = 0; i < ItemsInList(wavenames); i += 1)
		String name = StringFromList(i,wavenames)
		Wave/z w1= $name
		variable last = dimsize(w1,0)
			ABx=1 //calculate theta. ABx and ABy are set at 1,0. This will give a 1 unit long line along the x-axis.
			CDx=w1[last-1][0] //coordinate of last point
			ABy=0
			CDy=w1[last-1][1]
			theta=acos(((ABx*CDx)+(ABy*CDy))/(sqrt((ABx^2)+(ABy^2))*sqrt((CDx^2)+(CDy^2)))) //answer is in radians	
//			print name, " is ",theta," radians", "or" , theta*(180/pi), "degrees. last-1 =", CDx,",", CDy //remove // for debugging
			if (CDy<0)
				theta=theta								// execute if condition is TRUE
			else
				theta=(2*PI)-theta						// execute if condition is FALSE
			endif //if-elseif-endif statement checks if last point is above the x-axis and corrects the rotation.
			For (j = 0; j < last; j+=1)
				xcd = w1[j][0]
				ycd = w1[j][1]
				xprime = (xcd*(cos(theta)))-(ycd*(sin(theta)))
				yprime = (xcd*(sin(theta)))+(ycd*(cos(theta)))
				w1[j][0] = xprime
				w1[j][1] = yprime
			endfor
//			print "Now y is", ",", yprime 	//remove // for debugging. Should be ~0.
	endfor
End

This might be a lot easier

This might be a lot easier if you use the r2polar and p2rect functions and if you used complex waves instead of 2-column real waves.

--Jim Prouty
Software Engineer, WaveMetrics, Inc.

2D Rotation can be expressed

2D Rotation can be expressed simply as a 2x2 matrix and so the last loop in your code is a simple MatrixOP matrix-matrix multiplication (one line of code).

A.G.
WaveMetrics, Inc.

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