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I am looking for the most efficient way to plot a mesh using matplotlib given the following information, coordinates of each node, what nodes belong to each element, and the value each node has. Below I have some example data and image showing what the mesh looks like

nodeinfo=[[0.000,0.000],[1.000,0.000],[2.000,0.500],[0.000,1.000],
[1.000,1.000],[1.750,1.300],[1.000,1.700]]
elementInfo=[[1,2,5],[5,4,1],[2,3,6],[6,5,2],[4,5,7],[5,6,7]]
nodevalues=[1,2,1,2,7,4,5]

enter image description here

nodeinfo is the coordinates of each nodes(e.g. node 7 has coordinates (1,1.7)), elementInfo gives what nodes each element is composed of (e.g. element 3 has nodes 2,3,6), nodevalues gives the value of each node(e.g. node 5 has value 7).

Using this info how can I plot meshes with matplotlib with a colour gradient showing the different values of the nodes(if possible it would be great if there was a colour gradient between nodes as each element is linear).

Note If you want to use it have created a bit of code that organizes the information into node objects.

class node:
    # Initializer / Instance Attributes
    def __init__(self, number, xCord, yCord):
        self.number=number
        self.value=1
        self.isOnBoundary=False
        self.xCord=xCord
        self.yCord=yCord
        self.boundaryType=None
        self.element=[]

    #makes all class variables callable
    def __call__(self):
        return self

    def checkIfOnBoundary(self,boundarylist):
        # Checks if the node is on the boundary when it is invoked
        # If the node is not on the boundary then it is set to false

        if self.number in boundarylist:
            self.isOnBoundary=True
            self.boundaryType=boundarylist[self.number][0]
            if self.boundaryType == "Dirchlet":
                self.value=boundarylist[self.number][1]
        else:
            self.isOnBoundary=False

    def setElement(self,elementInfo):
        #given a list in the form [element1,element2,...,elementn]
        #where element1 is a list that contains all the nodes that are on that element
        for element in elementInfo:
            if self.number in element:
                self.element.append(elementInfo.index(element)+1)


    def setValue(self,value):
        # changes the value of the node
        self.value=value

    def description(self):
        return "Node Number: {}, Node Value: {}, Element Node Belongs to: {}, Is Node On the Boundary: {}".format(self.number, self.value, self.element, self.isOnBoundary)

nodeinfo=[[0.000,0.000],[1.000,0.000],[2.000,0.500],[0.000,1.000],
[1.000,1.000],[1.750,1.300],[1.000,1.700]]
elementInfo=[[1,2,5],[5,4,1],[2,3,6],[6,5,2],[4,5,7],[5,6,7]]
nodevalues=[1,2,1,2,7,4,5]

#create list of node objects which we will call on often
nodes=[]
for i in range(len(nodeinfo)):
    print(i)
    nodes.append(node(i+1,nodeinfo[i][0],nodeinfo[i][1]))
    nodes[i].setElement(elementInfo)

#print information related to each object
for phi in nodes:
    print(vars(phi))
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You might be interested in trying other visualization tools such as ParaView, Mayavi or vtki.

But, since the question is about Matplotlib, I would suggest that you use tricontour, tricontourf or tripcolor. They already accept the data in your format. Keep in mind that the enumeration of nodes starts from 0 in Python.

The following snippet show your data visualized.

import numpy as np
import matplotlib.pyplot as plt

nodes= np.array([
        [0.000, 0.000],
        [1.000, 0.000],
        [2.000, 0.500],
        [0.000, 1.000],
        [1.000, 1.000],
        [1.750, 1.300],
        [1.000, 1.700]])
eles = np.array([
        [1, 2, 5],
        [5, 4, 1],
        [2, 3, 6],
        [6, 5, 2],
        [4, 5, 7],
        [5, 6, 7]])
node_vals = [1, 2, 1, 2, 7, 4, 5]

x, y = nodes.T
plt.tricontourf(x, y, eles - 1, node_vals, 12)
plt.colorbar()
plt.show()

enter image description here

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  • $\begingroup$ Thanks for the answer I didn't know what functions / packages were available to me in python as I usually use Mathematica for plotting. I'll make sure to experiment with the other options. Just two small questions. What is the '.T' for? And how do I add a legend showing what the color values mean? $\endgroup$ – AzJ Apr 19 at 3:06
  • $\begingroup$ The .T is the transpose of the array, to get the columns with the x and y coordinates. $\endgroup$ – nicoguaro Apr 19 at 4:36

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