ddeabmDDEABM is variable step size, variable order Adams-Bashforth-Moulton PECE solver for integrating a system of first order ordinary differential equations [1-2]. It is a public-domain code originally developed in the 1970s-1980s, written in FORTRAN 77, and is available from Netlib (as part of the SLATEC Common Mathematical Library). DDEABM is primarily designed to solve non-stiff and mildly-stiff differential equations when derivative evaluations are expensive, high accuracy results are needed or answers at many specific points are required. It is based on the earlier ODE/STEP/INTRP codes described in [3-4].

DDEABM is a great code, but like many of the greats of Fortran, it seems to have been frozen in amber for 30 years. There are a couple of translations into other programming languages out there such as IDL and Matlab. It is also the ancestor of the Matlab ode113 solver (indeed, they were both written by the same person [5]). But, it looks like poor Fortran users have been satisfied with using it as is, in all its FORTRAN 77 glory.

So, I’ve taken the code and significantly refactored it to bring it up to date to modern standards (Fortran 2003/2008). This is more than just a conversion from fixed to free-form source. The updated version is now object-oriented and thread-safe, and also has a new event finding capability (there is a version of this code that had root-finding capability, but it seems to be based on an earlier version of the code, and also has some limitations such as a specified maximum number of equations). The new event finding feature incorporates the well-known ZEROIN algorithm [6-7] for finding a root on a bracketed interval. Everything is wrapped up in an easy-to-use class, and it also supports the exporting of intermediate integration points.

The new code is available on GitHub and is released under a permissive BSD-style license. It is hoped that it will be useful. There are some other great ODE codes that could use the same treatment (e.g. DLSODE/DVODE from ODEPACK, DIVA from MATH77, and DOP853 from Ernst Hairer).


  1. L. F. Shampine, H. A. Watts, “DEPAC – Design of a user oriented package of ode solvers”, Report SAND79-2374, Sandia Laboratories, 1979.
  2. H. A. Watts, “A smoother interpolant for DE/STEP, INTRP and DEABM: II”, Report SAND84-0293, Sandia Laboratories, 1984.
  3. L. F. Shampine, M. K. Gordon, “Solving ordinary differential equations with ODE, STEP, and INTRP”, Report SLA-73-1060, Sandia Laboratories, 1973.
  4. L. F. Shampine, M. K. Gordon, “Computer solution of ordinary differential equations, the initial value problem”, W. H. Freeman and Company, 1975.
  5. L. F. Shampine and M. W. Reichelt, “The MATLAB ODE Suite” [MathWorks].
  6. R. P. Brent, “An algorithm with guaranteed convergence for finding a zero of a function“, The Computer Journal, Vol 14, No. 4., 1971.
  7. R. P. Brent, “Algorithms for minimization without derivatives“, Prentice-Hall, Inc., 1973.
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One comment on “DDEABM
  1. Stefano says:

    Dear Jacob,

    my best compliments for this great project, it is very interesting!

    As you should know we are working on a similar project at https://github.com/Fortran-FOSS-Programmers/FOODIE

    It could be very helpful for us to have your support, e.g. the variable step size algorithm is yet missing into FOODIE Adams-Bashforth-Moulton solver. Are there any chances that you can join us?

    Anyway, great work, thank you very much for sharing with us!

    My best regards.

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