jcfried's profile - activity

After examining the denominator of C carefully i've come to the conclusion this is not a problem with roundoff. If i can figure out how to edit my original statement, i will remove that suggestion.

I am using sagemath.com for this test on 19 Feb 2014. I applied Simplify to

C = ((((K - 1)*L*sin(-(K - 1)*t/K) + (K - 1)) *
        ((K - 1)^2*L*sin(-(K - 1)*t/K)/K + (K - 1)*sin(t))) - 
         ((K - 1)*L*cos(-(K - 1)*t/K) - (K - 1)*cos(t)) *
         (-(K - 1)^2*L*cos(-(K - 1)*t/K)/K + (K - 1)*cos(t)))
     / ((((K - 1)*L*sin(-(K - 1)*t/K) + (K - 1)*sin(t))^2 +
       ((K - 1)*L*cos(-(K - 1)*t/K) - (K - 1)*cos(t))^2)^(3/2))

The result returned is about 10 times too small and the peaks shift position as K is increased toward 1. K and L are parameters that should be within (0,1). Plot with K = 0.42 and L = 0.22 in Sagemath demonstrates the problem.

Cs = ((K - 1)*L*cos((K - 1)*t/K) - (K - 1)*cos(t)) *
((K - 1)^2*L*cos((K - 1)*t/K)/K - (K - 1)*cos(t)) + 
((K - 1)*L*sin((K - 1)*t/K) - K + 1) *
((K - 1)^2*L*sin((K - 1)*t/K)/K - (K - 1)*sin(t))

As K approaches 0, the results more closely agree. Is this possibly a roundoff problem because of the numerator in C?

I verified the difference between the two using both Sagemath.com plot and Geogebra.

On Lion i ran into an additional problem. I had started the 10.6 server the night before and when i returned the next day, i could not connect to it through the browser because it kept asking for login id/passwd, but i don't have any id/passwd setup. I modified your suggestion slightly in order to get things to work for me. The problem appears to be that a server was running but not visible, so every attempt to restart the server simply caused a conflict with the other server that was already running.

do the following from a terminal window

ps A | fgrep -i sage
// Kill all sage process with a simple "kill <pid> <pid>" etc.
// CD to proper application version which is 10.6 for Lion.

// Now follow instructions provided earlier
cd /Applications/Sage-5.6-OSX-64bit-10.6.app/Contents/Resources/sage

./sage -notebook // This will open the worksheet in default browser.

I was not prompted for any login credentials and this opened my default workspace showing both of my existing worksheets.