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Solving & Tracing the Model

Contents

These commands calculate a steady-state hydraulic solution for the model, reload model data from disk, and trace connectivity or flow paths by color-coding connected features. Run a Trace before solving a model that isn’t behaving as expected — features left uncolored by a trace reveal a discontinuity, such as a closed valve or two features that only look connected on screen.

GDI Commands

Solve The Model

Calculates a steady-state solution for the model.

  1. Click the Solve icon in the lower-right corner of the GDI Window. The Solution Data screen is displayed.
  2. On the Solution Data tab, enter values and select options for calculating the steady-state solution.
  3. On the Pipe Sizing Control tab, enter values and select options to optimize pipe sizes, then click Solve & Calculate Pipe Sizes if you want sizing included in the solve.
  4. On the Other Settings tab, enter values and select options for any additional factors affecting the results.
  5. On the Model Notes tab, type any notes to save alongside the model.
  6. Click Solve to proceed, Close to save the settings and exit without solving, or Cancel to exit without saving or solving.
  7. If Solve was clicked, the Solution Log displays the results of each iteration and any exceptions found. Review the log, then click Close to return to the GDI Window.

Can also be run by selecting Solve Single Model from the Analysis menu, selecting Solve Model from the GDI Command List, or by typing SOLVE on the GDI Command Line.

Notes

  • If Display Favorite Results List Upon Completion is selected, the Favorite Results display in the Data Panel after the Solution Log is closed.
  • Model Notes can also be accessed anytime from the Model Notes item on the Edit menu.

Quick Solve A Model

Solves the model using the solution data values from the last time it was solved.

  1. Click the Quick Solve icon in the lower-right corner of the GDI Window. The results can be viewed in the GDI Window or one of the reports.

Can also be run by selecting the Quick Solve item from the GDI Command List or by typing QUICKSOLVE or QSOLVE on the GDI Command Line.

Regenerate The Model Data

Rereads the model data and background images from the disk file.

  1. Select the Regenerate Model Data item from the GDI Command List.
  2. A message asks whether to regenerate the model from the original data files. Click Yes to proceed (losing any changes since the last save) or No to end the command.

Can also be run by typing REGENERATE on the GDI Command Line.

Notes

  • All changes made since the last save will be lost.
  • Undo can restore up to the last ten changes to the model, but Regenerate The Model Data itself cannot be undone once run.

Trace

Performs a trace and color-codes the features along the route.

  1. Select the Create Trace item from the GDI Utilities branch of the GDI Command Tree. The Trace Specifications screen is displayed.
  2. Select a Trace Style and the type of feature to Start Trace At.
  3. Left-click the Trace Highlight Color panel to choose the color used for the traced features.
  4. Select or unselect Highlight Customers, Reset Feature Colors Before Tracing, and Blend Colors On Overlapping Trace Paths as needed.
  5. Select Create A Trace Results File to generate a results file, and choose which items to include in it; leave it unselected to trace without creating a file.
  6. Click Trace to proceed, or Cancel to close the screen without tracing.
  7. At the “Select Starting” prompt, left-click a feature of the specified type. The routine color-codes every connected feature per the specifications.

Can also be run by selecting the Trace item from the GDI Command List or by typing TRACE on the GDI Command Line.

Notes

  • This command is useful for verifying a model’s connectivity. Features left uncolored by the trace indicate a discontinuity in gas flow, such as a closed valve or two adjacent features that aren’t actually connected — running a trace before solving eliminates a possible source of error.
  • To save the trace color coding, use Save The Feature Colors; to return colors to how they were before the trace, use Reset The Feature Colors.
  • If Create A Trace Results File was selected, a results report is generated and saved once the trace completes — use View The Trace Results to view it.

Quick Trace

Performs a trace using the most recently used Trace Specifications.

  1. Select the Quick Trace item from the GDI Command List.
  2. At the “Select Starting” prompt, left-click a feature of the specified type. The routine color-codes every connected feature using the previous Trace Specifications.

Can also be run by typing QUICKTRACE or QTRACE on the GDI Command Line.

Trace & Update The Data

Performs a trace and updates a specified data value for every feature found along the route.

  1. Select the Trace & Update Data item from the GDI Command List. The Trace & Update Data Specifications screen is displayed.
  2. Select a Trace Style and the type of feature to Start Trace At.
  3. Left-click the Trace Highlight Color panel to choose the highlight color, and select or unselect Highlight Customers as needed.
  4. Select the data item to update from the Set list, and its new value from the Equal To list.
  5. Click Trace & Update to proceed, or Cancel to close the screen without tracing.
  6. At the “Select Starting” prompt, left-click a feature of the specified type. The routine color-codes every connected feature. A message may report the number of pipes selected — click Yes to continue updating the data, or No to return to the specifications screen.
  7. If Yes was clicked, a message may report how many records were updated. Click OK to clear it.

Can also be run by typing TRACEUPDATE on the GDI Command Line.

Notes

  • This is useful for updating features along a flow path — for example, if the pressure at a node is incorrect, this command can adjust pipe efficiencies along the major flow path between the supply point and that node, helping identify sections due for replacement or upgrading.
  • To save the trace color coding, use Save The Feature Colors; to return colors to how they were before the trace, use Reset The Feature Colors.

Notes & Considerations

  • The Solve icon (a balance scale) shows whether the model has been solved in its current configuration. Blue and balanced means a steady-state solution has been found; red and unbalanced means a change — like adding a customer or pipe, or changing a load — was made since the last solve. Left-clicking the icon in either state opens the Solution Data screen.

See Also

  • Adding Pipes & Nodes
  • Colors, Symbols, Sizes & Tool Palette
  • Views, Panning, Zooming & Plotting
  • GDI Utilities: Undo, Redo, Cancel & Housekeeping
  • Example: Selecting, Moving & Viewing Features
  • Example: Fittings, Panels & Palettes

FAQ

  • What kinds of tasks live under Analysis & Model Utilities?
    This subcategory covers running and interpreting the hydraulic analysis itself — solving and tracing the model — along with the calculations built on top of it (pressure drop, design factor, flow efficiency), routine load and supply-main housekeeping, and general-purpose model utilities like undo, redo, and node renumbering.
  • When should I use Solve versus Trace?
    Solve calculates the full hydraulic results for the model — pressures, flows, and related values at every feature. Trace instead follows the gas flow path through the system from a starting point without running a full solution, which is useful for quickly confirming connectivity or flow direction before committing to a full solve.
  • Where do I go if I made a change I want to undo, or need to renumber nodes after editing?
    Both live in GDI Utilities: Undo, Redo, Cancel & Housekeeping. Undo and Redo step backward and forward through your data and graphic changes, while Renumber The Nodes and the other housekeeping commands there handle cleanup tasks like reducing redundant nodes or resetting the numbering sequence after a lot of editing.
  • Can I calculate pressure drop or design factor without re-running a full solve?
    Yes — Calculating Pressures, Design Factor & Efficiency covers these as standalone calculations: Calculate Delta P (Linear), Calculate Delta P (Squared), Calculate The Design Factor, and Calculate The Flow Efficiency can each be run on their own rather than requiring a full model solve.
  • How do I bulk-update customer loads or move a batch of customers to a different supply main?
    Customer Loads, Supply Mains & Maintenance covers both. Multiply Customer Loads and Multiply Node Loads scale load values across a group at once, while Reassign A Customer’s Supply Main and Reassign The Customer’s Supply Main Numbers handle moving customers between supply mains.

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Updated on August 12, 2026

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