9.14.1 Top new questions this week

9.14.1.1 How do two equations multiply left by left equals right by right?
9.14.1.2 Measurement error propagation onto fitting-parameters
9.14.1.3 Filling area under line with lowest value
9.14.1.4 How can I make the following table quickly?
9.14.1.5 StreamPlot - streamlines are outside the plotting domain
9.14.1.6 Rank of singular, large, sparse matrices
9.14.1.7 Extract monomials with a certain structure from a given polynomial
9.14.1.1 How do two equations multiply left by left equals right by right?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283845

 eq1=x+2y==9 
eq2=3x+2y==10 
 
How to operate the multiplication of two equations to obtain: 
 (x+2y)(3x+2y)==90 
 
Simplify to obtain: 
<... 
[expression-manipulation] [algebraic-manipulation]
 
asked by csn899 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=68574 Score of 7
answered by David G. Stork https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9735 Score of 9
9.14.1.2 Measurement error propagation onto fitting-parameters

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283733

I have a dataset consisting of (t,y) Tuples, where each y has a known measurement error (standard deviation). I would like to fit a trapaze-function into the data and obtain the fitting paramaters and ... 
[probability-or-statistics] [fitting] [data] [physics] [error-propagation]
 
asked by Julius Debus https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=92352 Score of 7
answered by JimB https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=19758 Score of 5
9.14.1.3 Filling area under line with lowest value

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283874

How to use Fill but only under the line which has the lowest value on plot? Consider following code: 
... 
[plotting] [filling]
 
asked by Lechuu https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72560 Score of 5
answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 Score of 7
9.14.1.4 How can I make the following table quickly?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283780

Consider a table 
 Tabb = RandomReal[{0, 1}, {3, 2}]; 
 
I want to make the following table: 
... 
[list-manipulation] [performance-tuning] [syntax]
 
asked by John Taylor https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=41058 Score of 5
answered by Daniel Huber https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=46318 Score of 12
9.14.1.5 StreamPlot - streamlines are outside the plotting domain

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283721

I am trying to plot some streamlines, where the domain is given by a mesh. The results are good, but sometimes there are streamlines, that do not end at the boundary of the domain and are plotted a ... 
[plotting] [finite-element-method] [mesh]
 
asked by lemurman https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=86100 Score of 5
answered by cvgmt https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72111 Score of 2
9.14.1.6 Rank of singular, large, sparse matrices

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283946

I need to find the rank (and eventually do the Gaussian elimination) of a large, sparse, non-square matrix of integers. There are a few methods in Mathematica to find the rank of a non-square matrix (... 
[linear-algebra] [sparse-arrays]
 
asked by Albercoc https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72141 Score of 4
9.14.1.7 Extract monomials with a certain structure from a given polynomial

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=283951

I have a long polynomial such as 
 a x^2+ bx^2y+cx^2y^2 +d x^3y^4+e x^4y^3+f y^2+g xy^2 
 
Consider an example problem as follows: I want to output the monomials (along ... 
[polynomials] [algebraic-manipulation]
 
asked by cleanplay https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=8107 Score of 4
answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 Score of 4