Talk:Marginal rate of substitution

message: So how does MRS relate to relative price of goods ? are they the same ?
* No, MRS is unrelated to prices.  Instead, it's a matter of utility (as expressed by consumer preferences).  It's how much of one good you would be willing to give up for another good, if price weren't an issue.  So, if you had some X and some Y, and you could barter Y for X, then the MRS of X for Y would be how much Y you would be willing to give up for 1 unit of X.  --LostLeviathan 04:26, 16 January 2006 (UTC)
thread_title:  relative price of goods 

message: why are all the math functions not showing up in a web browser?  —Preceding unsigned comment added by 76.181.29.146 (talk) 05:32, 30 September 2008 (UTC)
thread_title:  math function display 

message: This article completely ignore that the mathematical operations involved might be forbidden. An utility function, as well as a production function might be "non-smooth" (for example non-differentiable, even non-continuous). In this case, what does the formulas become?
What would be the economic interpretation of such situations?
For example, 
U(x)=(u1 for x<=x1 and u2 for x>x1)
shows that at x1 we have a point of discontinuity
Also, for a production function of the type 
F(x,y)=min{x/a,y/b} 
we have non-differentiability points (for example the point (a,b)) 
So, in these situations, what becomes notions like MRS, TRS and elasticity of substitution?
The functions usually used to describe the production processes are inherited from econometrics, not from accurate modelling of the production process; the economic definition suggests that the production function is the result of an optimisation process... so, an intrinsic non-smooth character. 
Cristiann 23:17, 4 November 2006 (UTC)
replies: text: Not only might the utility function not be smooth, it might not correspond to a measure at all.  A pervasive problem with economics articles on Wikipedia is that the are written by editors who are only familiar with works in the Bentham-Jevons-Marshall tradition.  But see “The Austrian Theory of the Marginal Use and of Ordinal Marginal Utility” by J. Huston McCulloch in Zeitschrift für Nationalökonomie 37 (1973) for a mathematically formal treatment of MRS where utility cannot be fit to any measure. —SlamDiego 06:23, 24 April 2007 (UTC)
replies: text: Well behaved consumer preferences by definition must adhere to three conditions: monotonicity, convexity, and continuity. There are exception cases, which might reasonably be documented here, but those are finite and individually explainable. Generally, for the purposes of most decisions faced by average consumers, the conditions hold.  —Preceding unsigned comment added by 68.99.143.81 (talk) 10:20, 8 December 2010 (UTC)

text: Implicit differentiation assumes that y can be expressed as a function of x. If the marginal rate of substitution was derived using the implicit function theorem rather than using the total derivative, it would be clearer about when the implicit function theorem can bee applied. Woood (talk) 01:40, 27 March 2012 (UTC)
thread_title:  Remarks on Mathematical Operations 

message: Shouldn't MRSxy=MUy/MUx? instead of the inverse which is in the article? 128.86.148.253 (talk) 15:04, 10 November 2013 (UTC)
replies: text: Usage is inconsistent. E.g. http://www.econ.ohio-state.edu/jpeck/Econ501aL3.pdf agrees with you. I personally find it natural to retain the argument order from the utility function (since MRS depends on the same arguments).  But what is definitely wrong is to call MUx/MUy the marginal rate of substitution of x for y, as the article currently does.  It is obviously the marginal rate of substitution of y for x.  That is, it is the amount of y you would be willing to trade for one more unit of x. That is why it is declining in x. But many people have been careless about this usage. Cerberus (talk) 19:47, 22 April 2014 (UTC)
thread_title:  Wrong equation?