Explore: Troubleshooting Infeasibility in ALICE Pro

How to proceed if a user receives an 'infeasible schedule' error message?
This article provides suggestions on possible causes and solutions.

Not Enough Resources 

Causes

When the execution of the project requires more resources than the user has provided for a specific simulation. The scheduler will be unable to return any solutions and will, therefore, display an infeasibility error.

Examples

This usually happens when any of the following cases occur:

1- A task requires a minimum amount of Crews/Equipment/Material that is not provided in the simulation parameters.

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2- FaS/SaS/FaF/SaF type relationships force more than one task requiring one or more of the same resource resulting in a greater need of that resource than is provided.

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Solution

Try running a simulation with infinite resources first. If this works, we can then try to isolate which resource is causing the problem by running more simulations. If not, then we can move on to other infeasibility causes.

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Calendar Constraints

Causes

The calendar of one or more crews prevents working on certain days where work needs to happen

Examples

This usually happens when any of the following cases occur:

1- A Holiday Period Extends indefinitely

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2- Calendar constraints used to model deadline milestones which are not achievable in the current simulation

Solution

Double-check all workweeks and calendars.

Look for the Yellow dots and warning messages that flag problematic workweeks

Inadequate Crane Locations

Causes

A crane is required by some tasks but the crane is not available to service those tasks.

Examples

This usually happens when any of the following cases occur:

1- A Crane is defined and used in the Recipes with no set locations in the plan page

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2- Crane locations are set in the plan page but do not have all of the elements that are needed

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3- Two or more activities must happen at the same time but there is only one crane

(please refer to the FaS example in the “Not Enough Resource” Section)

Solution

The best way to solve this is to double-check crane positions and availability and make sure the whole project is covered.

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Alternatively, one can try to rule out if this is the cause of infeasibility by adding more crane positions than needed with extra-large radii. However, please remember to remove those additions when the testing is finished.

Missing Recipe Links

Causes

When creating recipes, one might forget to draw the precedence links from the previous element node to the first activity/activities or from the last activity/activities to the next element node.

Examples

This usually happens when any of the following cases occur:

1- A precedence link from the previous element node to the activity is missing

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2- A precedence link from an activity to the next element node is missing

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Solution

The best way to solve this is to double-check used recipes and look for missing links.

Corrupt Project

Although very unlikely, the infeasibility may be caused by the project being corrupt. The best way to find out if this is the case is to copy/clone the project plan and run your simulations on the newly created copy.

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Further Resources

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