# SimPEG.regularization.Smallness.f_m_deriv#

Smallness.f_m_deriv(m) csr_matrix[source]#

Derivative of the regularization kernel function.

For Smallness regularization, the derivative of the regularization kernel function with respect to the model is given by:

$\frac{\partial \mathbf{f_m}}{\partial \mathbf{m}} = \mathbf{I}$

where $$\mathbf{I}$$ is the identity matrix.

Parameters:
mnumpy.ndarray

The model.

Returns:
scipy.sparse.csr_matrix

The derivative of the regularization kernel function.

Notes

The objective function for smallness regularization is given by:

$\phi_m (\mathbf{m}) = \frac{1}{2} \Big \| \mathbf{W} \big [ \mathbf{m} - \mathbf{m}^{(ref)} \big ] \Big \|^2$

where $$\mathbf{m}$$ are the discrete model parameters defined on the mesh (model), $$\mathbf{m}^{(ref)}$$ is the reference model, and $$\mathbf{W}$$ is the weighting matrix. See the Smallness class documentation for more detail.

We define the regularization kernel function $$\mathbf{f_m}$$ as:

$\mathbf{f_m}(\mathbf{m}) = \mathbf{m} - \mathbf{m}^{(ref)}$

such that

$\phi_m (\mathbf{m}) = \frac{1}{2} \Big \| \mathbf{W} \, \mathbf{f_m} \Big \|^2$

Thus, the derivative with respect to the model is:

$\frac{\partial \mathbf{f_m}}{\partial \mathbf{m}} = \mathbf{I}$

where $$\mathbf{I}$$ is the identity matrix.