equation

问题 I'm making a calculator. And the challenge is not to use eval() . I made an array from all the inputs that looks like this: numbers = [1,1,'+',2,'*',3,'-','(',4,'*',5,'+',2,'/',5,')']; Then i convert this array to a string, remove the , and i get a string like this: numberString = "11+2*3-(4*5+2/5)"; So my question is, what is the way to correctly calculate the result of this equation without using eval() ? 回答1: Use an object to map operator strings to functions that implement the operator.

问题 I want to solve a set of equations, linear, or sometimes quadratic. I don't have a specific problem, but often, I have been in this situation often. It is simple to use wolframalpha.com, the web equivalent of Mathematica, to solve them. But that doesn't provide the comfort and convenience of an iPython shell. Is there a simple library to work on linear and quadratic equations from a python shell? Personally, I find it extremely convenient to use the Casio 991 MS scientific calculator. I know

问题 I want to develop a GUI application which displays a given mathematical equation. When you click upon a particular variable in the equation to signify that it is the unknown variable ie., to be calculated, the equation transforms itself to evaluate the required unknown variable. For example: a = (b+c*d)/e Let us suppose that I click upon "d" to signify that it is the unknown variable. Then the equation should be re-structured to: d = (a*e - b)/c As of now, I just want to know how I can go

问题 I hope you have some useful tip for me to approach the following task: I wrote some simple python snippet to plot probability density functions. In my particular case, let them represent class-conditional probabilities for some parameter x . So, I am wondering if there is an clever approach (i.e., module) in Python (maybe via a NumPy or SciPy function or method) to solve a simple equation for parameter x . E.g., pdf(x, mu=10, sigma=3**0.5) / pdf(x, mu=20, sigma=2**0.5) = 1 # get x Right now,

问题 I have the following model: which I've coded in R as: function(t,C,Ao,s,wd,ph) C + Ao * exp(-s*t) * cos(wd*t + ph) I want to use this equation to form a predictive model. However, I can't figure out how to either successfully run or plot this equation. I tried nls but got various errors (including those that warned me about a singular gradient . I looked here but I don't see where to go form here given that my model doesn;t seem to work. How can I model and graph this function in R? What I

问题 I need a library to solve Ax=b systems, where A is a non-symmetric sparse matrix, with 8 entry per row (and it might be quite big). I think a library that implements biconjugate gradient should be fine, but i can't find one that works (i've tried iml++, but there are some headers missing in the iml++/sparselib++ packages). Any tips? 回答1: There are standard ways of treating overdetermined systems. For example Wikipedia says this: A set of linear simultaneous equations can be written in matrix

问题 I need a library to solve Ax=b systems, where A is a non-symmetric sparse matrix, with 8 entry per row (and it might be quite big). I think a library that implements biconjugate gradient should be fine, but i can't find one that works (i've tried iml++, but there are some headers missing in the iml++/sparselib++ packages). Any tips? 回答1: There are standard ways of treating overdetermined systems. For example Wikipedia says this: A set of linear simultaneous equations can be written in matrix

问题 I need a library to solve Ax=b systems, where A is a non-symmetric sparse matrix, with 8 entry per row (and it might be quite big). I think a library that implements biconjugate gradient should be fine, but i can't find one that works (i've tried iml++, but there are some headers missing in the iml++/sparselib++ packages). Any tips? 回答1: There are standard ways of treating overdetermined systems. For example Wikipedia says this: A set of linear simultaneous equations can be written in matrix

问题 I've been trying to solve this implicit equation by using fzero in MATLAB. File that holds the code is named as "colebrook" and I've typed so far is as below. D = input('Please enter the pipe diameter in meters: '); V = input('Please enter the fluid velocity in m/s: '); rho = input('Please enter fluid density in kg/m^3: '); mew = input('Please enter fluid viscosity in kg/m*s: '); Re = D*V*rho/mew; eps = input('Enter absolute roughness in milimeters: '); eD = eps/(D*1000); a = fzero

问题 Scenario: An record was entered into the database. I am trying to figure out the following equations: How to get the number of hours since the record was added. How to get how many hours are left until midnight since the record was added. Given these times: Date / Time: 2012-08-22 20:11:20 Time Stamp: 1345684280 Midnight Tonight: 2012-08-23 00:00:00 Midnight Time Stamp: 1345698000 I feel like I'm on the right track. Just need some proper math to do the calculations? I am horrible at math. Any