12-16-2016, 02:57 PM

Yesterday I was doing an structures exam with my brand new HP prime.

At the end of one of the problems i had to solve a linear system of equations (KX=F) where K is the stiffness matrix. the problem came when i tried to solve it using the linear solver app, the system was something like:

5e11X+6e11Y=50000

6e11X+12e11Y=6000

the calculator just gave me X=0 Y=0.

I tried to solve it manually by calculating the inverse matrix of [[5e11,6e11],[6e11,12e11]] and the result was a matrix of zeros [[0,0],[0,0]].

after trying a couple of times I just took my old 50g from my backpack and solved the system without problems.

later in my house i tried again and always the result was a matrix of zeros when trying to invert a matrix with big coefficients, and also the same in my computer´s HP prime virtual calculator. reading the prime´s manual i found that the calculator does not manage numbers smaller than 1e-49 but its far away from the expected results of the equation system (values around 1e-4). also i found that there is no problem using the CAS mode or using approx([5e11,6e11],[6e11,12e11]]^-1) but i don't know why.

thanks god i had my 50g but i don't understand why i can't make the inverse matrix in the prime if i can do it even with a casio basic calculator.

pedro

civil engineering student

madrid (Spain)

At the end of one of the problems i had to solve a linear system of equations (KX=F) where K is the stiffness matrix. the problem came when i tried to solve it using the linear solver app, the system was something like:

5e11X+6e11Y=50000

6e11X+12e11Y=6000

the calculator just gave me X=0 Y=0.

I tried to solve it manually by calculating the inverse matrix of [[5e11,6e11],[6e11,12e11]] and the result was a matrix of zeros [[0,0],[0,0]].

after trying a couple of times I just took my old 50g from my backpack and solved the system without problems.

later in my house i tried again and always the result was a matrix of zeros when trying to invert a matrix with big coefficients, and also the same in my computer´s HP prime virtual calculator. reading the prime´s manual i found that the calculator does not manage numbers smaller than 1e-49 but its far away from the expected results of the equation system (values around 1e-4). also i found that there is no problem using the CAS mode or using approx([5e11,6e11],[6e11,12e11]]^-1) but i don't know why.

thanks god i had my 50g but i don't understand why i can't make the inverse matrix in the prime if i can do it even with a casio basic calculator.

pedro

civil engineering student

madrid (Spain)