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Manuscript Title: A Fortran program to fit diffusion models to field-gradient spin echo data.
Authors: E.D. von Meerwall, R.D. Ferguson
Program title: DIFFUS5
Catalogue identifier: ABNE_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 21(1981)421
Programming language: Fortran.
Computer: IBM 370/158 AP.
Operating system: OS/MVS.
RAM: 60K words
Word size: 32
Keywords: Nuclear physics, Diffusion, General experiment, Nuclear magnetic Resonance, Spin echo, Magnetic field gradient Method, Curve fitting, Restricted diffusion, Anisotropic diffusion, Multicomponent diffusion.
Classification: 17.4.

Nature of problem:
NMR spin echo attenuation in the presence of steady and/or pulsed magnetic field gradients is interpreted in terms of diffusion constants and parameters of inhomogeneity, anisotropy or relative intensity.

Solution method:
Least-squares curve fitting techniques are used to obtain two or three parameters of any of ten interpretive models to spinecho attenuation data. Error analysis and plot are provided.

Restrictions:
The present limit of 50 data points per case is easily extended. Five types of experiment and ten types of interpretation are provided for. Program is designed for easy modification.

Unusual features:
1) Arbitrary diffusing nuclear species, and various experiment types with arbitrary steady and pulsed gradient magnitudes and timmings are provided for;
2) Single and two-component diffusion, unattenuable echoes, spherically averaged anisotropic diffusion, and restricted diffusion with permeable or impereable barriers are available in at least one modification each;
3) Full error analysis gives uncertainties of all fitted parameters; chi-square permits checking the applicability of the model; a plot of data and fit is produced on the line printer.

Running time:
On the IBM 370/158 AP, the program compiles in about 19 s CPU; a case with 20 data points fitted with a restricted diffusion model takes up to 20 s CPU.