#!/usr/bin/env python
# coding: utf-8

# # Multiple energy terms of the same class
# 
# Here we demonstrate how to define multiple energy terms of the same class in the energy equation. For the sample, we choose a one-dimensional chain of magnetic moments.

# In[1]:


import random
import oommfc as mc
import discretisedfield as df
import micromagneticmodel as mm

p1 = (-10e-9, 0, 0)
p2 = (10e-9, 1e-9, 1e-9)
cell = (1e-9, 1e-9, 1e-9)
region = df.Region(p1=p1, p2=p2)
mesh = df.Mesh(region=region, cell=cell)


# The mesh is

# In[2]:


mesh.mpl(box_aspect=(10, 4, 4), figsize=(8, 8))


# Let us say that the system has an energy equation, which consists of two Zeeman energy terms.

# In[3]:


H1 = (0, 0, 1e6)
H2 = (1e6, 0, 0)

system = mm.System(name="multiple_terms")


# Now, if we try to add two Zeeman energy terms, we get an exception raised.

# In[4]:


system.energy = mm.Zeeman(H=(0, 0, 1e5)) + mm.Zeeman(H=(0, 1e5, 0))


# This is because different energy terms must have different names, so they can be uniquely identified. So, we have to give names to our energy terms:

# In[5]:


system.energy = mm.Zeeman(H=H1, name="zeeman1") + mm.Zeeman(H=H2, name="zeeman2")


# We need to define the system's magnetisation (`system.m`). We are going to make it random with $M_\text{s}=8\times10^{5} \,\text{Am}^{-1}$

# In[6]:


random.seed(1)

Ms = 8e5  # saturation magnetisation (A/m)


def m_fun(pos):
    return [2 * random.random() - 1 for i in range(3)]


system.m = df.Field(mesh, nvdim=3, value=m_fun, norm=Ms)


# Now, we can minimise the system's energy:

# In[7]:


md = mc.MinDriver()
md.drive(system)


# We expect that now all magnetic moments are aligned parallel or antiparallel to the anisotropy axis (in the $z$-direction).

# In[8]:


system.m.sel("y").mpl(
    figsize=(10, 3), scalar_kw={"clim": [-0.1, 0.1], "colorbar_label": "$m_y$"}
)


# We can see that magnetisation is aligned with the sum of fields `H1+H2`. Finally, let us have a look at the table:

# In[9]:


system.table.data


# We can see that energy terms are marked with the names we gave to energy terms when we defined the energy equation.