Convolution Integrals
- To: mathgroup at smc.vnet.net
- Subject: [mg16807] Convolution Integrals
- From: "Mortimer, Martin" <M.MORTIMER at CGIAR.ORG>
- Date: Tue, 30 Mar 1999 02:35:12 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Dear all: I am a new user of Mathematica and very much still on the learning curve, so I would be extremely grateful for some help. The background ----------------------- I need to do convolution integrals of various combinations of Gaussian (Normal) and Lognormal functions, sometimes in pairs, sometimes in threesomes and maybe more. It seems to me that the easiest way to do this is through the inverse fourier transform of the product of the fourier transforms of the functions. The problem ----------------- Here is a simple example of the code in the approach I have used so far. In[1]:= <<Statistics`ContinuousDistributions` In[2}:= <<Calculus`FourierTransform` In[3]:= dist1=NormalDistribution[10,3] Out[3]= NormalDistribution[10, 3] In[4]:= pdf1=PDF[dist1,x] Out[4]= 1 --------------------------- 2 (-10 + x) /18 3 E Sqrt[2 Pi] In[5]:= Plot[%,{x,0,20}] -Graphics- In[6]:= dist2=NormalDistribution[5,4] Out[6] = NormalDistribution[5, 4] In[7]:= pdf2=PDF[dist2,x] Out[7] = 1 -------------------------- 2 (-5 + x) /32 4 E Sqrt[2 Pi] In[8]:= trans1=FourierTransform[pdf1,x,s] Out[8] = 2 10 I s - (9 s )/2 E In[9]:= trans2=FourierTransform[pdf2,x,s] Out[9] = 2 5 I s - 8 s E In[10]:= conv=InverseFourierTransform[trans1 trans2] Out[10] = 2 15 I s - (25 s )/2 InverseFourierTransform[E ] Question : I seem to be able to get to the inverse transform alright but how do I plot the final distribution ? I would be very grateful for some clear code on how to do this that I can comprehend. I have looked in the archives and whilst there has been some discussion on this topic, I still cannot workout a way forward. For the curious, my work is concerned with the prediction of weed occurrence in rice fields and we are trying to develop a model that can predict the likelyhood of weed germination, establishment and ultimately yield loss. Thanking you in advance Martin Mortimer _____________________________________________________________________ Dr Martin Mortimer Weed Ecologist International Rice Research Institute, P. O. Box 3127 Makati Central Post Office(MCPO) 1271 Makati City Philippines Telephone: (63) 2 845 0563 / 0569 ext : - office 771 / 221 ; - home 249 E-mail: M.MORTIMER at CGIAR.ORG Fax: (63) 2 891 1292 or (63) 2 845 0606 Personal E-mail in UK: Greywing at compuserve.com "IRRI is one of 16 centers supported by the Consultative Group on International Agricultural Research (CGIAR). http://www.cgiar.org/irri <http://www.cgiar.org/irri> ." _____________________________________________________________________