Matplotlib.pyplot.streamplot() in Python - GeeksforGeeks

21 Oct, 2021
Stream plot is basically a type of 2D plot used majorly by physicists to show fluid flow and 2D field gradients .The basic function to create a stream plot in Matplotlib is:  
ax.streamplot(x_grid, y_grid, x_vec, y_vec, density=spacing)
Here x_grid and y_grid are arrays of the x and y points.The x_vec and y_vec represent the stream velocity of each point present on the grid.The attribute #density=spacing# specify that how much close the streamlines are to be drawn together. 
Let’s start by creating a simple stream plot that contains streamlines on a 10 by 10 grid.All the streamlines are parallel and pointing towards the right.The code below creates the stream plot containing horizontal parallel lines pointing to the right:  
Python3
# Import librariesimport numpy as npimport matplotlib.pyplot as plt # Creating datasetx = np.arange(0, 10)y = np.arange(0, 10) # Creating gridsX, Y = np.meshgrid(x, y) # x-component to the rightu = np.ones((10, 10)) # y-component zerov = np.zeros((10, 10)) fig = plt.figure(figsize = (12, 7)) # Plotting stream plotplt.streamplot(X, Y, u, v, density = 0.5) # show plotplt.show()
Output:  
Here, x and y are 1D arrays on an evenly spaced grid, u and v are 2D arrays of velocities of x and y where the number of rows should match with the length of y while the number of columns should match with x, density is a float value which controls the closeness of the stream lines. 
With the help of streamplot() function we can create and customize a plot showing field lines based on defined 2D vector field. Many attributes are available in streamplot() function for the modification of the plots. 
Python3
# Import librariesimport numpy as npimport matplotlib.pyplot as plt # Creating data setw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) # Creating plotfig = plt.figure(figsize = (12, 7))plt.streamplot(X, Y, U, V, density = 1) # show plotplt.show()
Output:  
Some of the customization of the above graph are listed below:Varying the density of streamlines – 
Python3
import numpy as npimport matplotlib.pyplot as pltimport matplotlib.gridspec as gridspec # Creating datasetw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) fig = plt.figure(figsize =(24, 20))gs = gridspec.GridSpec(nrows = 3, ncols = 2,                       height_ratios =[1, 1, 2]) # Varying the density along a# streamlineax = fig.add_subplot(gs[0, 0])ax.streamplot(X, Y, U, V,              density =[0.4, 0.8]) ax.set_title('Varying the density along a streamline') # show plotplt.tight_layout()plt.show()
Output:  
Varying the color along a streamline – 
Python3
import numpy as npimport matplotlib.pyplot as pltimport matplotlib.gridspec as gridspec # Creating datasetw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) fig = plt.figure(figsize =(24, 20))gs = gridspec.GridSpec(nrows = 3, ncols = 2,                       height_ratios =[1, 1, 2]) # Varying color along a streamlineax = fig.add_subplot(gs[0, 1])strm = ax.streamplot(X, Y, U, V, color = U,                     linewidth = 2, cmap ='autumn')fig.colorbar(strm.lines)ax.set_title('Varying the color along a streamline.') # show plotplt.tight_layout()plt.show()   
Output:  
Varying the line width along a streamline – 
Python3
import numpy as npimport matplotlib.pyplot as pltimport matplotlib.gridspec as gridspec # Creating datasetw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) fig = plt.figure(figsize =(24, 20))gs = gridspec.GridSpec(nrows = 3, ncols = 2,                       height_ratios =[1, 1, 2]) # Varying line width along a streamlineax = fig.add_subplot(gs[1, 0])lw = 5 * speed / speed.max()ax.streamplot(X, Y, U, V, density = 0.6,              color ='k', linewidth = lw) ax.set_title('Varying line width along a streamline') # show plotplt.tight_layout()plt.show()
Output:  
Controlling the starting points of streamlines – 
Python3
import numpy as npimport matplotlib.pyplot as pltimport matplotlib.gridspec as gridspec # Creating datasetw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) fig = plt.figure(figsize =(24, 20))gs = gridspec.GridSpec(nrows = 3, ncols = 2,                       height_ratios =[1, 1, 2]) # Controlling the starting points# of the streamlinesseek_points = np.array([[-2, -1, 0, 1, 2, -1],                        [-2, -1,  0, 1, 2, 2]]) ax = fig.add_subplot(gs[1, 1])strm = ax.streamplot(X, Y, U, V, color = U,                     linewidth = 2,                     cmap ='autumn',                     start_points = seek_points.T) fig.colorbar(strm.lines)ax.set_title('Controlling the starting\points of the streamlines') # Displaying the starting points# with blue symbols.ax.plot(seek_points[0], seek_points[1], 'bo')ax.set(xlim =(-w, w), ylim =(-w, w)) # show plotplt.tight_layout()plt.show()
Output:  
Streamlines skipping masked regions and NaN values – 
Python3
# Import librariesimport numpy as npimport matplotlib.pyplot as pltimport matplotlib.gridspec as gridspec # Creating datasetw = 3Y, X = np.mgrid[-w:w:100j, -w:w:100j]U = -1 - X**2 + YV = 1 + X - Y**2speed = np.sqrt(U**2 + V**2) fig = plt.figure(figsize =(20, 16))gs = gridspec.GridSpec(nrows = 3, ncols = 2, height_ratios =[1, 1, 2]) # Create a maskmask = np.zeros(U.shape, dtype = bool)mask[40:60, 40:60] = TrueU[:20, :20] = np.nanU = np.ma.array(U, mask = mask) ax = fig.add_subplot(gs[2:, :])ax.streamplot(X, Y, U, V, color ='r')ax.set_title('Streamplot with Masking') ax.imshow(~mask, extent =(-w, w, -w, w), alpha = 0.5,          interpolation ='nearest', cmap ='gray', aspect ='auto')ax.set_aspect('equal') # show plotplt.tight_layout()plt.show()
Output:  
Example: Stream plot to demonstrate the electric field due to two point charges.The electric field at any point on a surface depends upon the position and distance between the two charges: 
Python3
import sysimport numpy as npimport matplotlib.pyplot as pltfrom matplotlib.patches import Circle # Function to determine electric fielddef E(q, r0, x, y):    den = np.hypot(x-r0[0], y-r0[1])**3    return q * (x - r0[0]) / den, q * (y - r0[1]) / den # Grid of x, y pointsnx, ny = 64, 64x = np.linspace(-2, 2, nx)y = np.linspace(-2, 2, ny)X, Y = np.meshgrid(x, y) # Create a multipole with nq charges of# alternating sign, equally spaced# on the unit circle. # Increase the power with increase in chargenq = 2**1charges = []for i in range(nq):    q = i % 2 * 2 - 1    charges.append((q, (np.cos(2 * np.pi * i / nq),                        np.sin(2 * np.pi * i / nq)))) # Electric field vector, E =(Ex, Ey)# as separate componentsEx, Ey = np.zeros((ny, nx)), np.zeros((ny, nx)) for charge in charges:    ex, ey = E(*charge, x = X, y = Y)    Ex += ex    Ey += ey fig = plt.figure(figsize =(18, 8))ax = fig.add_subplot(111) # Plotting the streamlines with# proper color and arrowcolor = 2 * np.log(np.hypot(Ex, Ey))ax.streamplot(x, y, Ex, Ey, color = color,              linewidth = 1, cmap = plt.cm.inferno,              density = 2, arrowstyle ='->',              arrowsize = 1.5) # Add filled circles for the charges# themselvescharge_colors = {True: '#AA0000',                 False: '#0000AA'} for q, pos in charges:    ax.add_artist(Circle(pos, 0.05,                         color = charge_colors[q>0])) ax.set_xlabel('X-axis')ax.set_ylabel('X-axis')ax.set_xlim(-2, 2)ax.set_ylim(-2, 2)ax.set_aspect('equal') plt.show()
Output:  
 
saurabh1990aror
Python-matplotlib
Python
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