Common errors

This document explains the most common errors and provides solutions to fix them.

1. Could not find a version that satisfies the requirement concrete-python (from versions: none)

Error message: Could not find a version that satisfies the requirement concrete-python (from versions: none)

Cause: The installation does not work fine for you.

Possible solutions:

• Be sure that you use a supported Python version (currently from 3.8 to 3.11, included).

• Check that you have done pip install -U pip wheel setuptools before.

• Consider adding a --extra-index-url https://pypi.zama.ai/cpu/.

• Concrete requires glibc>=2.28, be sure to have a sufficiently recent version.

2. Only integers are supported

Error message: RuntimeError: Function you are trying to compile cannot be compiled with extra information only integers are supported

Cause: Parts of your program contain graphs that are not from integer to integer

Possible solutions:

• You can use floats as intermediate values (see the documentation). However, both inputs and outputs must be integers. Consider converting values to integers, such as .astype(np.uint64)

3. No parameters found

Error message: NoParametersFound

Cause: The optimizer can't find cryptographic parameters for the circuit that are both secure and correct.

Possible solutions:

• Try to simplify your circuit.

• Use smaller weights.

• Add intermediate PBS to reduce the noise, with identity function fhe.univariate(lambda x: x).

4. Too long inputs for table looup

Error message: RuntimeError: Function you are trying to compile cannot be compiled, with extra information as this [...]-bit value is used as an input to a table lookup with but only up to 16-bit table lookups are supported

Cause: The program uses a Table Lookup that contains oversized inputs exceeding the current 16-bit limit.

Possible solutions:

• Try to simplify your circuit.

• Use smaller weights.

• Look to the graph to understand where this oversized input comes from and ensure that the input size for Table Lookup operations does not exceed 16 bits.

• Use show_bit_width_constraints=True to understand bit widths are assigned the way they are.

5. Impossible to fuse multiple-nodes

Error message: RuntimeError: A subgraph within the function you are trying to compile cannot be fused because it has multiple input nodes

Cause: A subgraph in your program uses two or more input nodes. It is impossible to fuse such a graph, meaning replace it by a table lookup. Concrete will indicate the input nodes with this is one of the input nodes printed in the circuit.

Possible solutions:

• Try to simplify your circuit.

• Have a look to fhe.multivariate.

6. Function is not supported

Error message: RuntimeError: Function '[...]' is not supported

Cause: The function used is not currently supported by Concrete.

Possible solutions:

• Try to change your program.

• Check the corresponding documentation to see if there are ways to implement the function differently.

• Post your issue in our community channels.

7. Branching is not allowed

Error message: RuntimeError: Branching within circuits is not possible

Cause: Branching operations, such as if statements or non-constant loops, are not supported in Concrete's FHE programs.

Possible solutions:

• Change your program.

• Consider using tricks to replace ternary-if, as c ? t : f = f + c * (t-f).