concrete/docs/compilation/common_errors.md

Common errors

In this document, we list the most common errors, and mention how the user can 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 you have done pip install -U pip wheel setuptools before
• Consider adding a --extra-index-url https://pypi.zama.ai/cpu or --extra-index-url https://pypi.zama.ai/gpu, depending on whether you want the CPU or the GPU wheel.
• 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: This error can occur if parts of your program contain graphs which are not from integer to integer

Possible solutions:

• It is possible to use floats as intermediate values (see the documentation) but always, inputs and outputs must be integers. So, consider adding ways to convert to integers, such as .astype(np.uint64)

3. No parameters found

Error message: NoParametersFound

Cause: The optimizer was not able to find cryptographic parameters for the circuit, which 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: In your program, you use a table lookup where the input is too large, i.e., is more than 16-bits, which is the current limit

Possible solutions:

• Try to simplify your circuit
• Use smaller weights,
• Look to the MLIR to understand where this too-long input comes from

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: In your program, you have a subgraph using two nodes or more. It is impossible to fuse such a graph, i.e., to replace it by a table lookup. Concrete will show you where the different nodes are, with some 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: You are using a function which is not currently supported by Concrete

Possible solutions:

• Try to change your program
• Have a look to the documentation to see if there are ways to implement the function differently
• Ask our community channels

7. Branching is not allowed

Error message: RuntimeError: Branching within circuits is not possible

Cause: You are using branches in Concrete, it is not allowed in FHE program (typically, if's or non-constant loops)

Possible solutions:

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