Dan Piponi
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 Jul4 revised What is the geometric meaning of this integral? added 2 characters in body Jul3 answered What is the geometric meaning of this integral? Jul1 revised Second derivative of discrete function This isn't discrete mathematics Jul1 suggested approved edit on Second derivative of discrete function Jul1 awarded Enthusiast Jun30 comment Given a histogram, programatically, how do I find the normal distributions that comprise it? Jun30 comment What's wrong with having the same variable in the integrand as in the limits? @QiaochuYuan You point to the real issue. In principle $\int_0^x(\int_0^xx^3dx)x^4dx$ is unambiguous. But mathematicians like the abuse of notation that allows them to write what you just wrote and they find it worthwhile to sacrifice $\alpha$-equivalence to get it. (See en.wikipedia.org/wiki/Lambda_calculus#Alpha_equivalence .) I suspect that modern mathematics students with some computing experience may have slightly different ideas of what's reasonable. Jun28 answered Fibonacci Calculation using a larger matrix Jun27 revised Ways to study mathematics while commuting added 243 characters in body Jun27 answered Ways to study mathematics while commuting Jun27 comment Topologies on n-manifolds Do you mean other topologies? Or other topologies on $n$-manifolds? If the former then you'll find you need to understand the compact-open topology if you intend to study homotopy theory. en.wikipedia.org/wiki/Compact-open_topology Jun25 comment Where does this unit vector come from? There is a sphere here :-) The reason is that unit vectors are vectors of length 1, i.e. if you place the vector's tail at the origin its head lies on the unit sphere. So, in disguise, your question is "where does the vector $F_1$ meet a unit sphere?" Jun25 comment Is this mathematically correct? Well $v_1/v_2=13/15$ but $r_1/r_2=1$ for row 1. But suppose there are errors up to 10% in your voltage measurements, so, eg. $v_1$ is actually 2.8 and $v_2$ is actually 2.8, etc., then the relationship might hold exactly. Jun25 comment Is this mathematically correct? The relationship doesn't hold exactly. But if your voltage measurements are only accurate to 0.5V, say, then it is possible that the relationship holds. That's why experimenters give error bars when they publish results. Do you have some estimates of your uncertainty? Jun25 revised Convergence of two power series Type in title Jun25 suggested approved edit on Convergence of two power series Jun25 answered Complex analysis is more “real” than real analysis Jun24 comment What should I learn first, Mathematica or MatLab? Want to define a function? Stick an underscore after the argument names. Want to apply a function to some arguments? Use square brackets. Want to get the $i$th element of an array, use double square brackets. While one might quibble about what is or isn't natural, saying my claim that Mathematica notation "can look very unnatural" is outrageous is, well, interesting. Jun24 comment How to establish this inequality without using induction? Seeing as you defined the $a_n$ by induction it's going to be completely impossible to prove any non-trivial property of them without using induction in some form or other. Maybe you're trying to rule out one particular induction proof. Jun22 comment logic\math question If you look at the following link you'll see a number of examples that fit the pattern, some of which suggest answers other than 90: oeis.org/…