230 Matching Annotations
  1. Apr 2018
  2. Mar 2018
  3. Feb 2018
    1. Let’s use some common units as examples: gram (g), erg (erg), and solar mass per cubic megaparsec (Msun / Mpc33^3). g is an atomic, CGS base unit, erg is an atomic unit in CGS, but is not a base unit, and Msun/Mpc33^3 is a combination of atomic units, which are not in CGS, and one of them even has an SI prefix. The dimensions of g are mass and the cgs factor is 1. The dimensions of erg are mass * length$^2$ * time−2−2^{-2} and the cgs factor is 1. The dimensions of Msun/Mpc33^3 are mass / length33^3 and the cgs factor is about 6.8e-41.
  4. Jul 2017
  5. May 2017
    1. 1st order Eulerian numbers:Permutations

      Annotate math with math!

      $$\varepsilon = \frac{2}{h^3} \int_0^{p_F} \sqrt{p^2 c^2 + m^2 c^4} \cdot 4 \pi p^2 dp=$$

      $$\frac{8 \pi}{h^3} \frac{m c^2}{\lambda^3} \int_0^x \sqrt{1+y^2} \cdot y^2 dy $$

    1. The first review, by C. Hendricks Brown et al., poses the issues raised by the growingrecognition

      $$\varepsilon = \frac{2}{h^3} \int_0^{p_F} \sqrt{p^2 c^2 + m^2 c^4} \cdot 4 \pi p^2 dp=$$

      $$\frac{8 \pi}{h^3} \frac{m c^2}{\lambda^3} \int_0^x \sqrt{1+y^2} \cdot y^2 dy$$

  6. Apr 2017
  7. Jan 2017
  8. Nov 2016
  9. Oct 2016
    1. Sunil Singh asks us to stop promoting mathematics based on its current applications in business and science. Math is an art that should be enjoyed for its own sake.

      This reminded me of A Mathematician's Lament by Paul Lockhart. This is a 25-page essay which was later worked into a 140-page book. (And Sunil Singh has read at least one of them. He credits Lockhart in one of the replies.)

      It also reminds me of this article on the history of Gaussian elimination and the birth of matrix algebra. Newton's algebra text included instructions for solving systems of equations -- but it didn't have much practical use until later. (Silly word problems are as old as mathematics.)

  10. Sep 2016
  11. Jul 2016
  12. Mar 2016
  13. Feb 2016
  14. Jan 2016
  15. Mar 2015
  16. Jan 2015
    1. A function like f(x,y)=x+y is a function of two variables. It takes an element of R2, like (2,1), and gives a value that is a real number (i.e., an element of R), like f(2,1)=3. Since f maps R2 to R, we write f:R2→R. We can also use this “mapping” notation to define the actual function. We could define the above f(x,y) by writing f:(x,y)↦x+y. To contrast a simple real number with a vector, we refer to the real number as a scalar. Hence, we can refer to f:R2→R as a scalar-valued function of two variables or even just say it is a real-valued function of two variables. Everything works the same for scalar valued functions of three or more variables. For example, f(x,y,z), which we can write f:R3→R, is a scalar-valued function of three variables.

      f:R^2 \rightarrow R demek f(x,y)=z | Skalar-Değerli f f:R \rightarrow R^2 demek f(x)=(y,z) | VektörelDeğ f

  17. Sep 2013
    1. A computable Dedekind cut is a computable function which when provided with a rational number as input returns or ,

      This definition of computable Dedekind cut is wrong. The correct definition is that the lower and the upper cut be computably enumerable.