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RobotLocomotion / drake

Model-based design and verification for robotics.
https://drake.mit.edu
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Algebraic loop error message is unhelpful #7557

Closed ggould-tri closed 6 years ago

ggould-tri commented 6 years ago

I allegedly have an algebraic loop. However the error message is unhelpful:

*** 1 failure is detected in the test module "Master Test Suite"
Running 5 test cases...
unknown location(0): fatal error: in "TrajectoryTesterSmokeTest": std::logic_error: Algebraic loop detected in DiagramBuilder.
program/controller_analyzer/test/run_one_trajectory.cc(45): last checkpoint: "TrajectoryTesterSmokeTest" fixture ctor
ERROR: Non-zero return code '201' from command: Process exited with status 201

The error message should say (1) what systems constitute the loop, and (2) Direct the user toward DoHasDirectFeedthrough or the appropriate transmogrification boilerplate to make symbolic analysis work.

jwnimmer-tri commented 6 years ago

The "resolves" in #7564 message was in a comment, not the description, so the issue didn't auto-close.