Basic Pcolormesh - Linear Gradient (50x50 resolution)
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|1.00                                                                            |
| *                                                                              |
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|.800                                                                            |
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| *                                                                              |
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|.600                                                                            |
| *                                                                              |
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|                                                                                |
|.400                                                                            |
| *                                                                              |
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|                                                                                |
|.200                                                                            |
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| *              *              *               *              *               * |
|0              .200            .400            .600            .800        1.00 |
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                                  X coordinate
Y coordinate