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  "body": "\n## Summary\n\nThe directional derivative of a function $f$ at a point $a$ in the direction of a vector $v$ is a rate of change. It is the rate of change of $f$ when its input moves from $a$ along $v$.\nIt is the derivative at $t = 0$ of the function $t \\mapsto f(a + t v)$ of one variable.\nThe [[partial derivatives|09EGC6F8PT]] are the directional derivatives along the standard basis vectors.\n",
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  "name": "Directional derivative",
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