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[Wang Wang <question652185@xxxxxxxxxxxxxxxxxxxxx>]

New question #652185 on Yade:
https://answers.launchpad.net/yade/+question/652185

when i give a [0,0,0] strain to the Yade, the Yade gives back a stress that is not zero, and then give a zero strain to Yade, and Yade will give back a different stress. 
the question is when i set different young of the balls, i think the stress is no doubt different, however, when i give a strain like[1e-7,0,0],[0,1e-7,0],[0,0,1e-7] at the beginning of steps, the stress Yade get is different.
part of the code is as shown below:


		for b in O.bodies:
			b.material.young = 1.0001*17e10

      # because the send message can't reach the wanted precise 
     			
			ag = [0]*3               #  current - last   ie. the changed strain
			ag[0] = arr[0] - arrcc[0]
			ag[1] = arr[1] - arrcc[1]
 			ag[2] = arr[2] - arrcc[2]

			check[0] = 1 
			ns=100
			
			dstrain = utils.Matrix3(ag[0],ag[2],0,0,ag[1],0,0,0,0)      # the goal strain xx xy xz, yx yy yz, zx zy zz
			O.cell.velGrad=dstrain/(ns*O.dt)

			O.run(ns,True)                                               
	
			stressValue=utils.getStress()
			stressxx=stressValue[0,0]                                   # the return stress xx
			stressyy=stressValue[1,1]                                   # the return stress yy
			stressxy=(stressValue[0,1]+stressValue[1,0])/2              # the return stress xy = (xy + yx)/2

		msg=str(stressxx)+','+str(stressyy)+','+str(stressxy)
		print msg
		print 'transformation'
        	print O.cell.trsf                                           # the goal strain
    		c.send(msg)


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