# PTDBackendError { #phasic.exceptions.PTDBackendError }

```python
phasic.exceptions.PTDBackendError()
```

Backend not available error.

Raised when a specific computation backend (JAX, FFI, C++) is requested
but not available on the system.

## Examples {.doc-section .doc-section-examples}

```python
>>> from phasic.ffi_wrappers import compute_pmf_ffi
>>> pmf = compute_pmf_ffi(..., backend='ffi')
PTDBackendError: FFI backend requested but not available.
  FFI is currently disabled (see FFI_MEMORY_CORRUPTION_FIX.md).
  Available backends: ['jax', 'cpp']
```