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 ExpIntegralEi

 http://functions.wolfram.com/06.35.07.0003.01

 Input Form

 ExpIntegralEi[x] == Integrate[E^t/t, {t, -Infinity, x}, PrincipalValue -> True] /; Element[x, Reals]

 Standard Form

 Cell[BoxData[RowBox[List[RowBox[List[RowBox[List["ExpIntegralEi", "[", "x", "]"]], "\[Equal]", RowBox[List["Integrate", "[", RowBox[List[FractionBox[SuperscriptBox["\[ExponentialE]", "t"], "t"], ",", RowBox[List["{", RowBox[List["t", ",", RowBox[List["-", "\[Infinity]"]], ",", "x"]], "}"]], ",", RowBox[List["PrincipalValue", "\[Rule]", "True"]]]], "]"]]]], "/;", " ", RowBox[List["x", "\[Element]", "Reals"]]]]]]

 MathML Form

 Ei ( x ) 𝒫 - x t t t /; x TagBox["\[DoubleStruckCapitalR]", Function[Reals]] Condition ExpIntegralEi x 𝒫 t -1 x t t -1 x [/itex]

 Rule Form

 Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List["ExpIntegralEi", "[", "x_", "]"]], "]"]], "\[RuleDelayed]", RowBox[List[RowBox[List["Integrate", "[", RowBox[List[FractionBox[SuperscriptBox["\[ExponentialE]", "t"], "t"], ",", RowBox[List["{", RowBox[List["t", ",", RowBox[List["-", "\[Infinity]"]], ",", "x"]], "}"]], ",", RowBox[List["PrincipalValue", "\[Rule]", "True"]]]], "]"]], "/;", RowBox[List["x", "\[Element]", "Reals"]]]]]]]]

 Date Added to functions.wolfram.com (modification date)

 2001-10-29