Monday, August 13, 2012

Import .eps files in GIMP fail

Hey,

Today I am going to tell you how to overcome the problem of importing .eps files in GIMP software.
  • First, you have to have ghostscript (http://www.ghostscript.com/) installed in your system.
  • After that you have to set the environment variable GS_PROG set to the path of your ghostscript .exe location
    • to set the environment variable (Win7):
    • right click on My Computer -> Properties -> Advanced system settings -> Advanced tab -> Environment Variables
    • In system variables -> New
      • variable name : GS_PROG
      • variable value: e.g. E:\Program Files\gs\gs9.04\bin\gswin32.exe (insert the ghostscript path appropriately)
    • restart GIMP

LaTex \left and \right

Hi guys,

  • Today I will tell you what \left and \right means in LaTex.
  • Sometimes you need to enclose fractions in equations within tall brackets. That's where these \left and \right comes in to play.
    • syntax: \left c1 cmds \right c2
    • c1 and c2 are called enclosing symbols. Some of the frequently used enclosing symbols are: (  )  [  ]   \{   \}  |

        \left (\frac{a}{b} \right )




    • If you didn't use \left and \right, this is what you will get:
              (\frac{a}{b})
                   
    • Sometimes you may need such a symbol, but only at one side.
      • Then the syntax is: \left . cmds \right c2
      • That is, a period is used for the side where you do not use the enclosing symbol
                    \left . \frac{a}{b} \right |
                   
                       

    Thursday, August 2, 2012

    Standard deviation (SD), Standard error (SE) and Confidence Interval (CI)

    Hi all,

    I had a tough time understanding these 3 statistics and let me share what I understood with you guys.

    • The first thing we should know is that we will always be dealing with samples from a large population. For example, say we want to know the average height of a Japanese woman. We will measure the height of n=100 Japanese women and we will draw some conclusions about the entire Japanese women population.
      • Now, standard deviation (SD) of the 100 measurements will give us how our measurements vary around mean of the measurements.
      • the standard error (SE) (of the mean) will tell us the variability of our computed mean. I repeat; SD gave the variability of data around the mean and SE gives the variability of the computed mean, not the data around it.
      • finally, the confidence interval (CI) give us where the real mean of the large population might lie.

    • Now, how do we compute these 3 values?
      • SD is computed directly from our measurements.

      • SE is computed from SD.
                        This is how you get it.
        • if xi are n independent observations from a population that has a mean u, and standard deviation s then the variance of the total

    is ns^2 (because for two it will be s1^2 + s2^2)
        • The variance of T/n (mean) must be 1/n^2 * (ns^2) = s^2 / n
        • Thus, the standard deviation of T/n = s/(sqrt(n))

      • CIs are computed from the SE.
        • Say, we need a 95% CI, then
          • upper 95% limit =
          • lower 95% limit =
    1.96 comes from 0.975quantile of the normal distribution -- (100-95)/2%=0.975