**1. NAME AND TITLE**

REGN: Code System for Solving Nonlinear Systems of Equations via the Gauss-Newton
Method.

**AUXILIARY ROUTINE**

EXAMP: Test Program.

**2. CONTRIBUTOR**

Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia,
Bulgaria.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

REGN solves nonlinear systems of numerical equations in difficult cases: high nonlinearity, poor
initial approximations, a large number of unknowns, ill condition or degeneracy of a problem.

**5. METHOD SOLUTION**

REGN uses different variants of regularized iteration methods of the Gauss-Newton type.

**6. RESTRICTIONS OR LIMITATIONS**

The basic restriction is n < 200.

**7. TYPICAL RUNNING TIME**

The running time of the main algorithm depends upon the magnitude of the control E_{0}. The
numeric differentiation being used slows down the iteration procedure.

**8. COMPUTER HARDWARE REQUIREMENTS**

REGN is operable on the IBM 360/370 computers

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required.

**10. REFERENCE**

L. Alexsandrov, M. Drenska, and D. Karadjov, "The Programme Package REGN for Solving
Nonlinear Systems of Equations by Means of Regularized Methods of the Gauss-Newton Type,"
Informal report.

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one (1.2MB) DOS diskette which contains the source
code and test program.

**12. DATE OF ABSTRACT**

April 1984.

**KEYWORD**: DIFFERENTIAL EQUATION SOLVING