# S10005 {#S10005}

## Error Code {#error_code .section}

S10005

## Error Message {#error_message .section}

`The number of fitness function parameters must be greater than or equal to 2. RefId: S10005`

## Probable Causes {#probable_causes .section}

This error occurs when a fitness function takes an incorrect number of parameters.

**Note**: During training, GPLearn calculates fitness scores based on both the predicted value and the calculation result of the generated factor. Therefore, a user-defined fitness function must take at least 2 parameters.

## Solutions {#solutions .section}

Ensure that the fitness function takes at least 2 parameters.

**Parent topic:**[Error Code Reference](../../Troubleshooting/ErrorCode.md)

