Low-level Calculations Research Articles

Comparison of semiempirical and bsse corrected møller-plesset ab initio calculations on the direct addition of water to formaldehyde

Semiempirical AM1 and MNDO-PM3 as well as MP n/4-31G ( n=2–4) calculations were done on the hydrogen-bonded intermediate complexes and the transition state for the unassisted addition of one water molecule to formaldehyde in order to assess the similarity of the three models in the study of chemical reactions. The errors inherent in the low-level ab initio calculation were estimated both by extension of the basis set and by correction of the basis-set-superposition error (BSSE). Basis-set extension was performed by using MP n/6-31G( d, p) calculations. BSSE was corrected both at the Hartree-Fock and the post-Hartree-Fock level using the counterpoise method and accounting for deformation of the fragments. Drawbacks of the semiempirical methods are reported and analysed in relation to the ab initio results.

Parallel computations of optic flow in early image processing

Current calculations of optic flow from the motion of edge features in an image sequence are described, and used to illustrate the implementation of low-level image processing calculations on an SIMD (single instruction multiple data) machine. Most of the computational effort in the optic flow calculations is required for carrying out large, multidimensional, spatiotemporal convolutions over the image data, which may be carried out efficiently in parallel by mapping the image pixels into the processor array. Examples are given, showing that computation times consistent with video data input rates can easily be achieved. Later stages of the optic flow calculation, after moving edges features have been detected, are also carried out in parallel, although the computations are no longer completely uniform over the image data arrays. A VLSI processor array, embodying many of the features required for low-level image processing calculations, is briefly described.