Nexus: add CPU/GPU flags for batched code

[jtkrogel]

Proposed changes

Add support for key inputs that control where data is stored and operated on. Relevant operations are those that save memory by allocating work on the host/CPU instead of the GPU.

Currently, the only two (common user) relevant points of control I've identified are 1) orbitals are stored/evaluated on CPU instead of GPU, 2) matrix inverse is performed on CPU instead of GPU.

What type(s) of changes does this code introduce?

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Laptop

Checklist

• Yes. This PR is up to date with current the current state of 'develop'

[jtkrogel]

@ye-luo is this valid input? I want to know if other "gpu" etc flags need to be set for this to work (place/evaluate orbitals and matrix inverse on host).

<?xml version="1.0"?>
<simulation>
   <project id="vmc" series="0">
      <parameter name="driver_version"      >    batched         </parameter>
      <application name="qmcpack" role="molecu" class="serial" version="1.0"/>
   </project>
   <qmcsystem>
      <simulationcell>
         <parameter name="lattice" units="bohr">
                  6.74632230        0.00000000        0.00000000
                  0.00000000        6.74632230        0.00000000
                  0.00000000        0.00000000        6.74632230
         </parameter>
         <parameter name="bconds">
            p p p
         </parameter>
         <parameter name="LR_dim_cutoff"       >    15                 </parameter>
      </simulationcell>
      <particleset name="e" random="yes" randomsrc="ion0">
         <group name="u" size="16" mass="1.0">
            <parameter name="charge"              >    -1                    </parameter>
            <parameter name="mass"                >    1.0                   </parameter>
         </group>
         <group name="d" size="16" mass="1.0">
            <parameter name="charge"              >    -1                    </parameter>
            <parameter name="mass"                >    1.0                   </parameter>
         </group>
      </particleset>
      <particleset name="ion0">
         <group name="C" size="8" mass="21894.71359057295">
            <parameter name="charge"              >    4                     </parameter>
            <parameter name="valence"             >    4                     </parameter>
            <parameter name="atomicnumber"        >    6                     </parameter>
            <parameter name="mass"                >    21894.71359057295            </parameter>
            <attrib name="position" datatype="posArray" condition="0">
                     0.00000000        0.00000000        0.00000000
                     1.68658058        1.68658058        1.68658058
                     3.37316115        3.37316115        0.00000000
                     5.05974172        5.05974172        1.68658058
                     0.00000000        3.37316115        3.37316115
                     1.68658058        5.05974172        5.05974172
                     3.37316115        0.00000000        3.37316115
                     5.05974172        1.68658057        5.05974172
            </attrib>
         </group>
      </particleset>
      <wavefunction name="psi0" target="e">
         <sposet_builder type="bspline" href="MISSING.h5" tilematrix="1 -1 1 1 1 -1 -1 1 1" twistnum="0" source="ion0" version="0.10" meshfactor="1.0" gpu="no" precision="float" truncate="no">
            <sposet type="bspline" name="spo_ud" size="16" spindataset="0"/>
         </sposet_builder>
         <determinantset>
            <slaterdeterminant matrix_inverter="host">
               <determinant id="updet" group="u" sposet="spo_ud" size="16"/>
               <determinant id="downdet" group="d" sposet="spo_ud" size="16"/>
            </slaterdeterminant>
         </determinantset>
         <jastrow type="One-Body" name="J1" function="bspline" source="ion0" print="yes">
            <correlation elementType="C" size="7" rcut="3.37316115" cusp="0.0">
               <coefficients id="eC" type="Array">                  
0 0 0 0 0 0 0
               </coefficients>
            </correlation>
         </jastrow>
         <jastrow type="Two-Body" name="J2" function="bspline" print="yes">
            <correlation speciesA="u" speciesB="u" size="7" rcut="3.37316115">
               <coefficients id="uu" type="Array">                  
0 0 0 0 0 0 0
               </coefficients>
            </correlation>
            <correlation speciesA="u" speciesB="d" size="7" rcut="3.37316115">
               <coefficients id="ud" type="Array">                  
0 0 0 0 0 0 0
               </coefficients>
            </correlation>
         </jastrow>
      </wavefunction>
      <hamiltonian name="h0" type="generic" target="e">
         <pairpot type="coulomb" name="ElecElec" source="e" target="e"/>
         <pairpot type="coulomb" name="IonIon" source="ion0" target="ion0"/>
         <pairpot type="pseudo" name="PseudoPot" source="ion0" wavefunction="psi0" format="xml">
            <pseudo elementType="C" href="C.BFD.xml"/>
         </pairpot>
         <pairpot type="MPC" name="MPC" source="e" target="e" ecut="60.0" physical="no"/>
      </hamiltonian>
   </qmcsystem>
   <qmc method="vmc" move="pbyp">
      <parameter name="warmupSteps"         >    50              </parameter>
      <parameter name="blocks"              >    50              </parameter>
      <parameter name="steps"               >    10              </parameter>
      <parameter name="subSteps"            >    3               </parameter>
      <parameter name="timestep"            >    0.3             </parameter>
      <parameter name="useDrift"            >    no              </parameter>
   </qmc>
</simulation>

[prckent]

By eye this looks correct and consistent with the manual.

[ye-luo]

LGTM.

[jtkrogel]

OK, good. Let's move forward then.

[prckent]

Test this please