DISTANCE MATRICES There is an increasing interest in the chemical community in under- standing not just the static structure of chemicals, but the ways in which they move and vibrate. Currently, the large volume of data being generated makes it very difficult to interpret. The Graphics group has generated a number of tools to provide the chemist with a variety of representations of a moving molecule. The data being demonstrated are avian-Pancreatic-Polypeptide (aPP) which have been loaded into a relational data base. When the animation is being run, the user may control the angle of view with the 3D-joystick, the scale and panning with the tablet, and the speed and direction of motion with program function keys. Distance matrices give a pictorial representation of the changing inter-atomic distances when the aPP molecule vibrates. In concept, they are similar to the matrices sometimes found in the back of a road atlas which give the mileages between various cities. The matrix is square, symmetrical, and has a leading diagonal of zeros as this represents the distance between each atom and itself. Because of the symmetry, only half of the matrix is displayed. The matrices are plotted with the height of the intersections above the base proportional to the distance between the corresponding atoms. Only the top 'triangle' is normally shown to simplify the picture. The resulting matrix is a useful one for looking at the overall structure of the molecule. When the distance matrices are animated, the peaks begin to rise and fall as the inter-atomic distances change. In order to clarify the representation only the alpha-carbons atoms are shown. The peaks indicate atoms which are close together (this is the inverse of traditional distance matrices). This is consistent with a helical shape which brings the alpha-carbons into close proximity. NOTE: If there is a problem with the 'movie' (e.g. VG is hanging, screen remains blank, unexpected image appears etc.), press PF1, return to demo menu and retry. PF1 causes execution of the 'instant' command 'hv' (halt Vector General).