Prompt Engineering For Exasim

AI tools perform best when the prompt is specific enough to constrain the physics, numerics, files, and validation. A vague prompt such as "Create a Navier-Stokes solver" leaves too many choices unspecified: formulation, mesh, boundary conditions, nondimensional parameters, discretization, initial conditions, outputs, and verification.

Anatomy Of A Strong Prompt

Include these parts when asking an AI assistant to modify Exasim:

Prompt part	Why it matters
Objective	Defines the concrete deliverable.
Location	Prevents files from being created in the wrong tree.
Reference example	Anchors style, APIs, dimensions, and solver settings.
Physics model	Identifies ModelC, ModelD, ModelW, or a built-in model.
Geometry and units	Prevents scale and boundary-tag mistakes.
Boundary conditions	Essential for well-posed PDEs.
Initial conditions	Required for transient runs and nonlinear convergence.
Parameters	Defines physicsparam ordering and dimensions.
Outputs	Specifies solution files, VTK, QoI, plots, or mesh images.
Verification	Tells the AI how success should be checked.

Weak Versus Strong Prompt

Weak:

Create a Navier-Stokes solver.

Strong:

Create a new Exasim MATLAB example under
Exasim/examples/NavierStokes/my_flat_plate.
Use examples/NavierStokes/flatplate2d as the reference.
Solve steady compressible Navier-Stokes in 2D with ModelD.
Geometry:
- rectangular flat-plate domain in meters: x in [0, 1.0], y in [0, 0.4]
- plate wall is the bottom boundary y = 0
- inlet is x = 0, outlet is x = 1.0, farfield is y = 0.4
- use a boundary-layer quadrilateral mesh refined toward y = 0
Use gamma = 1.4, Pr = 0.72, Re = 5000, Mach = 0.3.
Generate pdeapp.m and pdemodel.m only.
Keep MPI disabled, porder = 2, and saveParaview = 1.
Boundary conditions:
- inlet: uniform freestream
- wall: no-slip adiabatic wall
- outlet: pressure outflow
- farfield: freestream
Run the example if possible and report residual convergence and generated files.

The strong prompt supplies directory, reference example, model class, geometry, parameters, solver settings, boundary conditions, output expectations, and verification.

Prompt Template

Create or modify <thing> in <exact path>.

Reference examples:
- <path/to/similar/example>

Physical problem:
- PDE/model:
- Geometry and units:
- Boundary conditions:
- Initial conditions:
- Physical parameters and ordering:

Numerical requirements:
- ModelC/ModelD/ModelW or built-in model:
- porder/pgauss:
- steady or time-dependent:
- CPU/GPU/MPI assumptions:
- output and postprocessing:

Implementation requirements:
- files to create or edit:
- do not modify:
- preserve compatibility with:

Verification:
- commands to run:
- expected outputs:
- numerical checks:

Useful Constraints To Add

• "Make minimal changes and explain affected files before editing."
• "Use the existing Exasim frontend APIs; do not invent new fields."
• "Use existing examples as style references."
• "If information is missing, state assumptions explicitly."
• "Run mkdocs build --strict for documentation changes."
• "Run the smallest representative example before scaling up."

Avoid These Patterns

• Asking for multiple unrelated changes in one prompt.
• Omitting boundary conditions.
• Omitting units or coordinate ranges.
• Asking for "optimize the GPU code" without profiler output.
• Asking for "fix convergence" without residual history, mesh, parameters, and boundary information.
• Accepting generated code without compiling or validating it.