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POEM_041.md

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POEM ID: 041
Title: Add expressions to ExecComp after instantiation
authors: [robfalck]
Competing POEMs: N/A
Related POEMs: N/A
Associated implementation PR: #1977

Status

  • Active
  • Requesting decision
  • Accepted
  • Rejected
  • Integrated

Motivation

Almost all OpenMDAO components allow for IO to be added after instantiation. Currently, ExecComp does not; the handling of all IO is done in setup. There are situations where an expression needs to be added at setup time.

Description

This POEM proposes to add a new method to ExecComp: add_expr. Add_expr will take the same form as ExecComp initialization:

def add_expr(expr, **kwargs)

To make it usable during the configure step of setup, add_expr will immediately add the necessary IO and declare the relevant partials for the given expression.

Example

import openmdao.api as om
exec_comp = om.ExecComp()
exec_comp.add_expr('y = sin(x)', y={'shape': (5,)}, x={'shape': (5,)})

Detecting inconsistent variable metadata

If added after the above example, the following should raise an error:

exec_comp.add_expr('z = cos(x)', z={'shape': (6,)}, x={'shape': (6,)})
ValueError: Input x has multiple values for metadata: 'shape'