c......Example 2: Cartesian to spherical polar coordinates convertor c23456 program ex2 c implicit none c double precision cart(3),polar(3) double precision pi integer i c c..... Assign the value of pi c pi = 3.14159265358979d0 c c..... Read in the three Cartesian coordinates from the screen c print *, 'Enter (x,y,z) on one line separated by commas' read *,cart(1),cart(2),cart(3) c c.....The above line can also be written using an implicit do loop c read *,(cart(i), i = 1,3) c c.....NOTE: There are a variety of ways of converting from Cartesian to c..... spherical polar coordinates. The method illustratd below is c..... just one. c c..... Calculate the r vector c..... Assign the r vector to polar(1) c polar(1) = sqrt(cart(1)**2+cart(2)**2+cart(3)**2) c c..... Calculate the value of theta using the fact that z = r*cos(theta) c..... Assign theta to polar(2) c polar(2) = acos(cart(3)/polar(1)) c c..... Calculate the value of phi using the fact that c..... x = r*sin(theta)*cos(phi) c polar(3) = acos(cart(1)/(polar(1)*sin(polar(2)))) c c..... Output the results to the keyboard c print *,'Spherical polar coordinates are (angles in radians):' print *, ' r = ',polar(1) print *, ' theta = ',polar(2) print *, ' phi = ',polar(3) c c..... Remember that the trigonometric units are by default radians c..... To convert to degrees you need a value for pi, c..... Recall: 2*pi radians = 360 degrees c polar(2) = polar(2)/pi*180.0d0 polar(3) = polar(3)/pi*180.0d0 c c..... Output the result to the keyboard c print *,'Spherical polar coordinates are (angles in degrees):' print *, ' r = ',polar(1) print *, ' theta = ',polar(2) print *, ' phi = ',polar(3) c end
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Last updated August 8, 2003.