A two dimensional finite element program has been translated from Pascal to Fortran to run on an ICL PERQ single user computer under the PNX operating system. Many improvements and extensions have been incorporated, including automatic meshing algorithms. Extensive use is made of the PERQ's excellent interactive graphics capabillttes zo set up models, boundary conditions, etc and to post-process "the results.
post.processing, boundaries, Poisson equation, meshing, single user compuZar
The ICL ~ERQ single user~omputer is 'one ,o~f:agrow.ing number,~)f machines which offer, ;in addition to a large RAM and ahigh capacity Winchester hard disc, fast h~h resolution interactive graphics. These features make such a computer an ideal workstation for the pre-and postprocessing of data for finite element programs for very large models, and will permit complete finite element analyses to be performed wholly within the machine for smaller problems having, perhaps, a few thousand degrees of freedom.
This paper describes an interactive program which began as a project to use the facilities available, to set up and solve the Laplace and Poisson equations for 2D and axisymmetric problems by the finite element method. Originally this program (called APPLE -A Program for Poisson and Laplace Equations) was written in Pascal to run under the Three Rivers PERQ operating system (POS) 1 , but has been converted during the past year to Fortran 77 to run under ICL PERQ UNIX (PNX). The opportunity has been taken to extend the program to provide added convenience to the user.
Fast, interactive graphics means that, to a large extent, the user can be freed from the chore of controlling the problem with a keyboard. Coordinates, region boundaries, ctc may be entered by using the PERQ tablet puck to position a screen cursor. The program flow may be controlled by means of pop-up menus -at each appropriate stage a rectangular menu appears on the screen, and the user uses the puck to make a choice. After choosing, the menu disappears and the region which it occupied is returned to its original state. Programs of this type often make use of fixed menus, which remain on view. The advantage of the pop-up menu is ergonomic -the user does not need to shift the puck to another position, but pops up the menu at the puck's current position.
In the POS Pascal version, the calls to graphics primitives were embedded in the procedures. The UNIX system is largely written in C, hence the PNX graphics primitives are accessible only via functions written in C. ft was decided to