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  2. $XD = DX$ then $X$ is diagonal - Mathematics Stack Exchange

    math.stackexchange.com/questions/761734/xd-dx-then-x-is-diagonal

    To prove the statement, simply calculate XD = DX entrywise. One gets xijdj =dixij for every i ≠ j. Your proof is wrong and incomplete. While the diagonal entries of D are distinct, one of them may be zero. So, one of the "eigenvector" you produce may be the zero vector. In addition, you said " X = DXD−1 hence X is diagonal".

  3. What do the symbols d/dx and dy/dx mean?

    math.stackexchange.com/questions/340744

    28. The symbol. dy dx. means the derivative of y with respect to x. If y = f(x) is a function of x, then the symbol is defined as. dy dx =limh→0 f(x + h) − f(x) h. and this is is (again) called the derivative of y or the derivative of f. Note that it again is a function of x in this case. Note that we do not here define this as dy divided ...

  4. Derivative of sigmoid function $\\sigma (x) =...

    math.stackexchange.com/questions/78575

    In my AI textbook there is this paragraph, without any explanation. The sigmoid function is defined as follows $$\sigma (x) = \frac{1}{1+e^{-x}}.$$ This function is easy to differentiate

  5. Differentiate $f (x)=x^TAx$ - Mathematics Stack Exchange

    math.stackexchange.com/questions/312077

    In our case f(x) = xTAx and σ(t) = x + th, f ′ (x; h) = lim t → 0 (x + th)TA(x + th) − xTAx t f ′ (x; h) = xTAh + hTAx. Since A is symmetric and we have the follwing: f ′ (x; h) = xTAh + hTAx = xTAh + xTATh f ′ (x; h) = xT(A + AT)h. So the differential/gradient is simply 2xTA. f ′ (x; h) = 2xTAh. Share. Cite.

  6. Actually in MathTrain's definition, dx d does describe a mapping, namely inv ∘ d dx ∘ inv where inv: (x ↦ f(x)) ↦ (x ↦ 1 f (x)). And while inv is not a linear function, applying it twice "cancels" its nonlinearity out (well, except for the factor 0, but that could be defined by continuity), so dx d is even linear, hence an operator.

  7. how to solve this optimization problem with functions?

    math.stackexchange.com/questions/477638/how-to-solve-this-optimization-problem...

    As a somewhat simple-minded start, $\begin{align} &\int_0^{s^{-1}(1-s(0))} \left(s(0)[s^{-1}(1-s(0))]+\int_0^{\theta} (1-s^{-1}(1-s(x)))dx\right) d \theta +\int_{s ...

  8. solving the integral of $e^{x^2}$ - Mathematics Stack Exchange

    math.stackexchange.com/questions/1242056/solving-the-integral-of-ex2

    3. The integral which you describe has no closed form which is to say that it cannot be expressed in elementary functions. For example, you can express ∫x2dx in elementary functions such as x3 3 + C. However, the indefinite integral from (−∞, ∞) does exist and it is π−−√ so explicitly: ∫∞ −∞e−x2 = π−−√. Note the ...

  9. and then I tried substituting: t = sinxcosx and got ∫ tdt 2(1 − 2t2)√1 − 4t2. Another way would maybe be to make two integrals: ∫ 1 sin4x + cos4xdx = ∫ 1 (1 − √2sinxcosx)(1 + √2sinxcosx) dx = 1 2∫ 1 1 − √2sinxcosxdx + 1 2∫ 1 1 + √2sinxcosxdx. ... and again I tried t = tanx 2 (4th degree polynomial) and t = √ ...

  10. Evaluate double integral - Mathematics Stack Exchange

    math.stackexchange.com/questions/3488537/evaluate-double-integral-%e2%88%acxydxdy

    Given the straight line boundary off center, there is no advantage using the polar coordinates. Instead, integrate as follows, A = ∫5 − 4∫√25 − y2 5 − y 3 xydxdy. where the lower and upper limits -4 and 5 are the y -intersections of the line with the circle. The x -integration leads to. A = 1 2∫5 − 4y(25 − y2 − (5 − y)2 9 ...

  11. What does the dx mean in an integral? [duplicate]

    math.stackexchange.com/questions/1329131

    The $\Sigma$ sign is a sigma and stands for "sum". In an integral you take the limit as $\delta x$ goes to zero. So we replace the sigma with another type of s: $\int$. And the $\delta$ gets changed to a d. So it is now written: $\int f (x) dx $. and it is the "integral of f (x) with respect to x". But the dx doesn't mean anything on it's own.