Source code for pylops.basicoperators.Pad

import numpy as np

from pylops import LinearOperator

[docs]class Pad(LinearOperator): r"""Pad operator. Zero-pad model in forward model and extract non-zero subsequence in adjoint. Padding can be performed in one or multiple directions to any multi-dimensional input arrays. Parameters ---------- dims : :obj:`int` or :obj:`tuple` Number of samples for each dimension pad : :obj:`tuple` Number of samples to pad. If ``dims`` is a scalar, ``pad`` is a single tuple ``(pad_in, pad_end)``. If ``dims`` is a tuple, ``pad`` is a tuple of tuples where each inner tuple contains the number of samples to pad in each dimension dtype : :obj:`str`, optional Type of elements in input array. Attributes ---------- shape : :obj:`tuple` Operator shape explicit : :obj:`bool` Operator contains a matrix that can be solved explicitly (``True``) or not (``False``) Raises ------ ValueError If any element of ``pad`` is negative. Notes ----- Given an array of size :math:`N`, the *Pad* operator simply adds :math:`\text{pad}_\text{in}` at the start and :math:`\text{pad}_\text{end}` at the end in forward mode: .. math:: y_{i} = x_{i-\text{pad}_\text{in}} \quad \forall i=\text{pad}_\text{in},\ldots,\text{pad}_\text{in}+N-1 and :math:`y_i = 0 \quad \forall i=0,\ldots,\text{pad}_\text{in}-1, \text{pad}_\text{in}+N-1,\ldots,N+\text{pad}_\text{in}+\text{pad}_\text{end}` In adjoint mode, values from :math:`\text{pad}_\text{in}` to :math:`N-\text{pad}_\text{end}` are extracted from the data: .. math:: x_{i} = y_{\text{pad}_\text{in}+i} \quad \forall i=0, N-1 """ def __init__(self, dims, pad, dtype="float64"): if np.any(np.array(pad) < 0): raise ValueError("Padding must be positive or zero") self.dims = dims self.pad = pad self.reshape = False if isinstance(self.dims, int) else True if self.reshape: self.dimsd = [dim + p[0] + p[1] for dim, p in zip(dims, pad)] else: self.dimsd = dims + pad[0] + pad[1] self.shape = (, self.dtype = np.dtype(dtype) self.explicit = False def _matvec(self, x): if self.reshape: y = x.reshape(self.dims) y = np.pad(y, self.pad, mode="constant") else: y = np.pad(x, self.pad, mode="constant") return y.ravel() def _rmatvec(self, x): if self.reshape: y = x.reshape(self.dimsd) for ax, pad in enumerate(self.pad): y = np.take(y, np.arange(pad[0], pad[0] + self.dims[ax]), axis=ax) else: y = x[self.pad[0] : self.pad[0] + self.dims] return y.ravel()