From 9dbe8daad0455e1d4d134e993d5cd64d684276e5 Mon Sep 17 00:00:00 2001
From: Benoit Chevallier-Mames <benoit.chevalliermames@zama.ai>
Date: Mon, 17 Jun 2024 17:56:30 +0200
Subject: [PATCH] docs(frontend): adding a section for most common errors

closes #https://github.com/zama-ai/concrete-internal/issues/719
---
 docs/SUMMARY.md                   |  1 +
 docs/compilation/common_errors.md | 81 +++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 docs/compilation/common_errors.md

diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index 33c815fdc..b6aed9bad 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -30,6 +30,7 @@
    * [Multi parameters](compilation/multi_parameters.md)
 * [Compression](compilation/compression.md)
 * [Reusing arguments](compilation/reuse_arguments.md)
+* [Common errors](compilation/common_errors.md)
 
 ## Execution / Analysis
 
diff --git a/docs/compilation/common_errors.md b/docs/compilation/common_errors.md
new file mode 100644
index 000000000..33cba273f
--- /dev/null
+++ b/docs/compilation/common_errors.md
@@ -0,0 +1,81 @@
+# 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`
+- 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](../core-features/floating_points.md#floating-points-as-intermediate-values)) 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)`
+
+
+