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Hello,
I am using comsol 4.1 to study the magnetic response of a structure.
My 3D model consists of a set of square cross-sectioned wires starting at one of the big environment box domain and ending at the opposite one (so the run through the air box). In the middle there's some magnetic material I would like to study. I set all the conditions as in the "?Integrated Square-Shaped Spiral Inductor" model in the model gallery. I use free triangular mesh and Comsol meshes it with no pbs. When I solve it it gives me this error:

Attempt to evaluate negative power of zero.
- Function: ^
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod2.mef.murzz@VDN$mod2.curlA2z
- Defined as: (dmod2.mat6.def.MUR_dx1((sqrt((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2)))/unit_T_cf))*(((mod2.mef.Bz*2)*(0.5*((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2))^(-0.5))))*(1/unit_T_cf)))
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod2.mef.murinvzz@VDN$mod2.curlA2z
- Defined as: (((dmod2.mat6.def.MUR_dx1((sqrt((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2)))/unit_T_cf))*(((mod2.mef.Bz*2)*(0.5*((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2))^(-0.5))))*(1/unit_T_cf))))*((-1)/(mod2.mef.murzz^2)))
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod2.mef.Hz@VDN$mod2.curlA2z
- Defined as: (((((((dmod2.mat6.def.MUR_dx1((sqrt((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2)))/unit_T_cf))*(((mod2.mef.Bz*2)*(0.5*((((mod2.mef.Bx^2)+(mod2.mef.By^2))+(mod2.mef.Bz^2))^(-0.5))))*(1/unit_T_cf))))*((-1)/(mod2.mef.murzz^2))))*mod2.mef.Bz)+mod2.mef.murinvzz)*(1/mu0_const))
Failed to evaluate expression.
- Expression: d(d((-mod2.mef.Hx*test(mod2.curlA2x)-mod2.mef.Hy*test(mod2.curlA2y)-mod2.mef.Hz*test(mod2.curlA2z)+mod2.mef.Jx*test(mod2.A2x)+mod2.mef.Jy*test(mod2.A2y)+mod2.mef.Jz*test(mod2.A2z))*(dvol),{test@4}),mod2.curlA2z)


I tried resizing the environment domain and the mesh, I set the conductivity of air to 1 as indicated in the "?Integrated Square-Shaped Spiral Inductor" documentation, I tried switching to the other module called magnetic fields (mf), and same stuff.
When I remove the magnetic structure it solves with no problems. The magnetic structure is a collection of rectangular prisms with the material set to soft iron (no losses), without changing anything.

Any suggestions to make it solve INCLUDING the magnetic structure?

Thanks so much!
Giuseppe Schiavone