Merge branch 'gpu-syntax' into 'master'

Add single quotes and warning message.

See merge request !164

content/guides/submitting_jobs/submitting_cuda_or_openacc_jobs.md

@@ -5,7 +5,7 @@ description =  "How to submit GPU (CUDA/OpenACC) jobs on HCC resources."
 
 ### Available GPUs
 
-Crane has four types of GPUs available in the **gpu** partition. The
+Crane has four types of GPUs available in the `gpu` partition. The
 type of GPU is configured as a SLURM feature, so you can specify a type
 of GPU in your job resource requirements if necessary.
 
@@ -46,6 +46,13 @@ a feature. To run on K40 GPUs for example:
 --partition=gpu --gres=gpu --constraint=gpu_k40
 {{< /highlight >}}
 
+{{% notice info %}}
+You may request multiple GPUs by changing the` --gres` value to
+-`-gres=gpu:2`. Note that this value is **per node**. For example,
+`--nodes=2 --gres=gpu:2 `will request 2 nodes with 2 GPUs each, for a
+total of 4 GPUs.
+{{% /notice %}}
+
 The GPU memory feature  may be used to specify a GPU RAM amount either independent of architecture, or in combination with it.
 For example, using
 
@@ -54,20 +61,17 @@ For example, using
 {{< /highlight >}}
 
 will request a GPU with 16GB of RAM, independent of the type of card (K20, K40, P100, etc.).  You may also
-request both a GPU type _and_ memory amount using the `&` operator.  For example,
+request both a GPU type _and_ memory amount using the `&` operator (single quotes are used because `&` is a special character).  
+For example,
 
 {{< highlight batch >}}
---partition=gpu --gres=gpu --constraint=gpu_32gb&gpu_v100
+--partition=gpu --gres=gpu --constraint='gpu_32gb&gpu_v100'
 {{< /highlight >}}
 
 will request a V100 GPU with 32GB RAM.
 
-
-{{% notice info %}}
-You may request multiple GPUs by changing the` --gres` value to
--`-gres=gpu:2`. Note that this value is **per node**. For example,
-`--nodes=2 --gres=gpu:2 `will request 2 nodes with 2 GPUs each, for a
-total of 4 GPUs.
+{{% notice warning %}}
+You must verify the GPU type and memory combination is valid based on the [available GPU types.]({{< relref "submitting_cuda_or_openacc_jobs/#available-gpus" >}}).  Requesting a nonexistent combination will cause your job to be rejected with a `Requested node configuration is not available` error.
 {{% /notice %}}
 
 ### Compiling