<｜begin▁of▁sentence｜>### Instruction:
As an ENT specialist, you have a patient who has been experiencing issues with their hearing, balance, and vocal problems. To better understand the possible interconnected issues, you need to visualize a network associated with diseases of the ear, nose, and throat using networkx and save the visualization as an image ('graph_visualization.png') for further analysis and explanation to the patient. The graph description is available in a GML file ('example.gml'). In the visualization, you are required to utilize a gradient color scheme to visually distinguish between different vertices, highlighting the various disorders and diseases that may be interconnected.
### Response:
import igraph as ig
import cairocffi as cairo

# Read the graph
filename = 'example.gml'
g = ig.Graph.Read_GML(filename)

# Create a Cairo surface to draw on with a specified size
width, height = 600, 400
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
ctx = cairo.Context(surface)

# Create the plot with the specified dimensions
colors = ['#fc9272', '#de2d26', '#a50f15']  # Define your color gradient
g.vs['color'] = colors  # Assign colors to vertices

plot = ig.Plot(surface, bbox=(width, height))
plot.add(g)
plot.redraw()

# Save the plot as a PNG file
png_path = 'graph_visualization.png'
surface.write_to_png(png_path)
<|EOT|>
